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What is the cause of the spots on this leaf?

What is the cause of the spots on this leaf?


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On a hiking trip to the Alps I found trees whose leaves showed those spots you see on the picture. I am curious about what the cause is.

Higher resolution pictures of front and back side.


This is a "Tar Spot" disease usually found in Europe and North America. It mostly affects the Maple tree leaves. Tar spot is caused by 'Rhytisma acerinum' a plant pathogen fungus. This pathogen does not seem harm to tree but disturbs the leaves as it finds a suitable condition in summer with bit of wetness. It enters the leaves through stoma and then creates yellow lesions of various sizes over the leaf area which later gradually turns into brown-black tar colored spot. It reduces the photosynthesis process of leaves and thus creating more wide dark spots on the leaves. After sometime the leaves will fall.

Entire detail is available in the Wikipedia link with the detail of the pathogen. (Add some more info if you find this detail not enough)


Cherry leaf spot 101: Understanding Blumeriella jaapii biology and management

Cherry leaf spot causes significant economic loss in Michigan each year. Management has become more complicated due to the introduction of novel fungicides and resistance issues.

Cherry leaf spot, caused by the ascomycete Blumeriella jaapii (Rehm) Arx, is arguably the most damaging fungal pathogen of tart cherry, and has the potential to significantly reduce profits for growers in the Great Lakes region of the United States. Cherry leaf spot primarily affects foliage and, as a result, reduces the photosynthetic ability of the tree. Infected tart cherry leaves will turn yellow and defoliate prematurely if the disease is not effectively controlled (Photo 1). Sweet cherry leaves yellow but are retained. Less than 50 percent defoliation by early September is considered acceptable control in Michigan.

Photo 1. Symptoms of cherry leaf spot infection. Photo credit: George Sundin, MSU Department of Plant Pathology

When significant defoliation occurs before harvest, fruit can become soft and immature, have low soluble solids and ripen unevenly (Photo 2). Significant defoliation can be quantified based on the standard that at least two leaves are needed to effectively ripen each cherry on tart trees. Following two or more years with significant defoliation early in the season, trees are susceptible to winter injury due to the loss of photosynthates and therefore store carbohydrates in roots. Blossom production may also be reduced for at least two subsequent years.

Photo 2. Montmorency tree defoliated by CLS causingunderdeveloped fruit. Photo credit: Erin Lizotte, MSU Extension.

B. jaapii overwinters on fallen leaves on the orchard floor and produces apothecia, or sexual spore-bearing structures, in the spring. The primary infection period may last two to six weeks depending on conditions. Optimal apothecial development occurs between 6 to 16°C (43 to 61°F) with ascospore discharge increasing with temperature between 8 to 30°C (46 to 86°F). Ascospore release occurs as tissue dries following the thorough wetting of mature asci. Germination occurs on the surface of the leaf and infection occurs through the leaf stomata. Leaves remain susceptible throughout the growing season, contrary to the in vitro evidence of ontogenic, or age-related resistance in leaves. Following infection, acervuli develop on the underside of the infected leaf and produce a visible mass of white conidia. Conidia are dispersed from leaf to leaf by wind or rain and the infection cycle can be repeated several times during a single season, depending on conditions. The conidial stage was the basis for the development of an effective infection model by Eisensmith, an adaptation of which is still in use today. Visit Michigan State University&rsquos Enviro-weather web site for more information.

All commercially cultivated cherry cultivars are susceptible to cherry leaf spot, although less susceptible cultivars have been found. The primary method of management is through fungicide application, with five to seven applications recommended per season depending on disease pressure. The most common fungicides used to control cherry leaf spot include chlorothalonil, captan, strobilurins and several sterol demethylation inhibitors such as fenbuconazole, tebuconazole, myclobutanil and fenarimol. Salts containing the Cu 2+ ion, such as copper hydroxide or copper sulfate, and dodine are also used.

In lieu of innate resistance to pathogenic fungi in tart cherry cultivars (Prunus cerasus L.) and sweet cherry cultivars (Prunus avium L.), cultural practices and sanitation are frequently helpful in controlling fungal diseases, but ultimately fungicides are required to maximize yield and quality. Intensive fungicide use provides a potent selective pressure that increases the frequency of fungicide-resistant isolates in a pathogen population. As the frequency of resistant isolates increases, a resistant subpopulation may develop. This subpopulation can increase over time and lead to a reduced level of disease control in that population. This is commonly referred to as practical field resistance, and is defined as the point at which the frequency and levels of resistance are great enough to limit the effectiveness of disease control in the field.

In the late 1960&rsquos, the first reports of sporadic fungicide resistance were documented in Europe. In 1969, reduced sensitivity ofVenturia inaequalis (Cke.) Wint., the causal agent of apple scab, to dodine was reported in New York. This report was the first documented case of field resistance to any fungicide used in fruit production in the United States. By the late 1980&rsquos, over 60 resistant fungal genera in hundreds of crop systems had been documented. Currently, all of the systemic fungicide groups (sterol inhibitors, benzimidazoles, strobilurins, phenylamides and dicarboximides) have been affected by resistance.


Plants with Spotted Leaves

Fungal leaf spot can be found in your outdoor garden as well as on your houseplant. Spotted leaves occur when fungal spores in the air find a warm, wet, plant surface to cling to. As soon as that microscopic spore gets comfortable in its new home, sporulation (the fungal method of reproduction) occurs and the tiny brown fungal leaf spot begins to grow.

Soon the circle grows large enough to touch another circle and now the fungal leaf spot looks more like a blotch. Eventually the leaf turns brown and falls to the soil where the spores sit and wait for the next available warm, wet, plant surface so the fungal leaf spot process can begin again.


Management Strategies

Holly leaf spots seldom cause significant damage to the health of infected plants. Maintain plant vitality with proper fertilization, irrigation during dry periods, mulching, and attention to soil pH levels is the best way to minimize these diseases. Prune plants to promote, sunlight penetration, air circulation and rapid drying of foliage. Also, minimize leaf wetness by irrigating before midday so the leaves dry rapidly in the afternoon. Removal of infected fallen leaves reduces the amount of the inoculum present for new infections. Holly leaf spot diseases are usually more severe after wet springs, but they rarely warrant fungicide controls. Fungicide sprays protect the new green shoots and leaves. Begin sprays as the buds swell and reapply 2-3 more times at label intervals to maintain protection during vulnerable periods.


Viruses and Virus Diseases of Vegetables in the Mediterranean Basin

Benoît Moury , Eric Verdin , in Advances in Virus Research , 2012

III Thrips-Transmitted Tospoviruses

The genus Tospovirus in the family Bunyaviridae includes important species of plant viruses with pleomorphic particles (80–120 nm) enveloped by a double-membrane layer and which contain tripartite single-stranded RNAs, designated L, M, and S ( De Haan et al., 1990, 1991 German et al., 1992 Law et al., 1992 ). The negative L RNA (8.9 kb) consists of a single open reading frame (ORF) in the viral complementary sense that encodes a 331-kDa protein containing RdRp motifs required for virus replication ( Adkins et al., 1995 De Haan et al., 1991 Van Poelwijk et al., 1997 ). The ambisense M RNA (4.8 kb) ( Kormelink et al., 1992 Law et al., 1992 ) consists of two ORFs that encode a 36-kDa nonstructural protein, NSm, in the viral sense, and a 127.4-kDa precursor for G1 and G2 glycoproteins in the viral complementary sense. NSm protein may be involved in cell-to-cell movement ( Storms et al., 1995 ), whereas G1 and G2 structural glycoproteins are included in the outer membrane of the virion generating spikes ( Adkins et al., 1996 Law et al., 1992 ) and are essential for thrips transmission ( Sin et al., 2005 ) probably through their interaction with thrips receptor proteins. The ambisense S RNA (2.9 kb) ( De Haan et al., 1990 ) encodes two proteins: the 52.4-kDa nonstructural NSs and the 29-kDa structural nucleocapsid protein (NP) in the viral and the complementary senses, respectively. The NSs protein is associated to fibrous inclusions in infected plant cells ( Kormelink et al., 1991 ) and has been shown to be a suppressor of posttranscriptional gene silencing ( Takeda et al., 2002 ).

Tospoviruses cause great losses in many economically important crops, including pepper, worldwide. Two virus species belonging to this genus infect pepper in the Mediterranean surroundings: Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV) ( Fig. 4 ). In pepper, TSWV is more prevalent than INSV, which infects mainly ornamentals ( Daughtrey et al., 1997 ). TSWV is also the most widespread, occurring in all countries of the Mediterranean region, even if it has not been confirmed in a few ones (Morocco and Tunisia) and has one of the largest host ranges among plant viruses ( Parrella et al., 2003 ). INSV seems to be restricted to France, Spain, Italy, and Israel and has not been described in North Africa. Several studies have shown that high temperatures (> 30 °C) promote TSWV infections ( Llamas-Llamas et al., 1998 Roggero et al., 1999 ) and the resistance of some pepper cultivars can be impaired under continuous high temperatures, resulting in systemic infection of the plants ( Black et al., 1991 Moury et al., 1998 ). By contrast, high temperatures decrease the systemic movement of INSV in Capsicum chinense and Capsicum annuum ( Roggero et al., 1999 ), which may explain the rarity of natural INSV infections in pepper crops in the Mediterranean area. Most of the time, symptoms caused by TSWV are similar to those due to INSV. Symptoms in C. annuum include stunting and yellowing of the whole plant, mosaic or necrotic spots, and curling of the leaves. Infected fruits often show deformations, necrotic ring patterns, and arabesque-like discolorations.

Figure 4 . Unrooted neighbor joining phylogenetic tree of the coat protein gene of tospoviruses. The arrows indicate pepper-infecting tospoviruses and tospoviruses that do not infect solanaceous plants are shaded in gray. Bootstrap percentages above 50% are shown. The scale bar indicates branch lengths in substitutions per nucleotide.

In nature, tospoviruses are transmitted from plant to plant almost exclusively by thrips (order Thysanoptera family Thripidae) in a persistent and multiplicative manner. TSWV, like INSV, is transmitted mainly by the western flower thrips (Frankliniella occidentalis) ( De Angelis et al., 1994 ), but other Thripidae, like Thrips tabaci and Frankliniella intonsa, can also participate to the spread of TSWV. Outbreaks of TSWV in Europe have been associated to the introduction of F. occidentalis from western USA in the early 1980s. An estimation of the speed of spread across Europe and northern Africa was 229 ± 20 km/year ( Kirk and Terry, 2003 ). The western flower thrips not only is established in glasshouses but also outdoors in areas with mild winters like the Mediterranean basin. Vectors can acquire tospoviruses only during larval stages while both larval (late stage) and adult thrips can transmit the virus. For TSWV, it has been shown that the ability to acquire and transmit tospoviruses was lost during the development to adults, probably because of the formation of a midgut barrier ( Ullman et al., 1992 ). No transovarial transmission has been reported for tospoviruses.

Various management procedures have been undertaken during the past decades to reduce the spread of tospoviruses. Control of vectors is complicated by the high fecundity of thrips and their capacity to develop insecticide resistances. The wide host range of tospoviruses, including weeds that constitute virus reservoirs, increases the difficulties to control the disease. The application of sanitation measures must be intensified in glasshouses, particularly the eradication of weeds inside and outside the cultivated area, the use of blue, more attractive, or yellow sticky cards to monitor the presence of winged adults thrips ( Matteson and Terry, 1992 Roditakis et al., 2001 ), the regular examination of the crops, and the eradication of infected plants. Biological control of thrips on pepper crops relies on the use of predatory mites like Neoseiulus cucumeris or predatory bugs (Orius spp.) ( Hatala Zseller and Kiss, 1999 Maisonneuve and Marrec, 1999 ) and can decrease the virus inoculum pressure. Genetic resistance has been developed on several plants species, especially tomato and pepper, to control the dissemination of viral diseases associated with tospoviruses. Concerning pepper, several C. chinense lines possess monogenic resistances conferred by the Tsw gene ( Boiteux, 1995 Moury et al., 1997 ) and have been used to breed C. annuum cultivars resistant to TSWV. Tsw controls HR against most TSWV isolates and prevents the virus movement from cell to cell ( Soler et al., 1999 ). It is not efficient against other tospovirus species like INSV.

Appearance of TSWV isolates adapted to the Tsw resistance has been observed first in laboratory conditions ( Black et al., 1991 Moury et al., 1997 ). In southern Europe, breakdowns of the resistance were observed very rapidly after the release of Tsw-carrying cultivars and have been described in 1999 in Italy and Spain ( García-Arenal and McDonald, 2003 ). The TSWV genetic factors involved in the breakdown of the Tsw resistance are still under investigation. Some authors designated the NSs nonstructural protein ( Margaria et al, 2007 Tentchev et al., 2011 ), whereas others demonstrated the role of the NP encoded by the N gene ( Lovato et al., 2008 ). A way to reconcile these findings would be that two separate TSWV genes interact with the Tsw resistance in pepper: a gene which induces the resistance process (potentially the NP gene which was shown to be a specific elicitor of hypersensitive response in Tsw pepper plants) and a second gene which is targeted by the defence reactions and where resistance-breaking mutations can occur (presumably the NSs gene).

Resistance to the thrips vectors is known in several pepper (C. annuum) accessions and affects the level of feeding damage, host preference, and host suitability for reproduction. Some authors have shown that TSWV transmission was little affected by vector resistance under experimental conditions ( Maris et al., 2003 ). Owing to the lower reproduction rate and the lower attraction of thrips for resistant pepper plants, these authors supposed that beneficial effects might be expected from resistant cultivars under field conditions. Relationships between TSWV and its vectors are complex since TSWV-infected pepper plants increase attraction for female thrips compared to noninfected plants, thus improving TSWV dissemination ( Maris et al., 2004 ). Also, male thrips infected with TSWV fed more than uninfected males, with a threefold increase of noningestion probes during which they salivate, thus increasing the probability of virus inoculation ( Stafford et al., 2011 ).

Finally, Polygonum ringspot virus, a new tospovirus species, was recently discovered in northern and central Italy in wild buckwheat (Polygonum convolvulus) and in P. dumetorum ( Ciuffo et al., 2008 ). Polygonum ringspot virus is closely related to Tomato yellow ring virus ( Fig. 4 ), a tospovirus infecting ornamental and vegetable crops in Iran ( Hassani-Mehraban et al., 2007 Rasoulpour and Izadpanah 2007 ). Although this virus was found only in wild plants and was not detected in neighboring crops, it was shown to infect a large number of solanaceous plants, including pepper, after mechanical inoculation in laboratory conditions and could be a future threat for Italian and Mediterranean horticulture.


Leaf Spot Disease of Trees and Shrubs

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Even the most conscientious and hardworking gardener is likely to encounter leaf spot problems on trees and shrubs. The seemingly sudden appearance of brown or black blotches on leaves and defoliation are common occurrences. It is unlikely that most homeowners will make it through a season without at least one problem with a leaf spot pathogen.


Rose Downy Mildew image by Joan Allen

Symptoms of leaf spots vary depending upon the causal agent. Although leaf spots can be caused by air pollutants, insects and bacteria et al., most are a result of infection by pathogenic fungi. Once into the leaf, the fungi continue to grow and leaf tissue is destroyed. Resulting spots vary in size from that of a pinhead to spots that encompass the entire leaf. Dead areas on the leaves are usually brown, black, tan or reddish in color. Occasionally the necrotic areas have a red or purple border. Partial to complete defoliation may occur under favorable conditions for the causal fungus.

Many of the leaf spot fungi have a similar life cycle. The causal fungus over-winters on fallen leaves. In the spring, during or following a rain, spores produced by the fungus are discharged and carried by the wind and splashing rain to newly emerging leaves. The spore germinates and penetrates these young tender leaves causing infection. In a few days to several weeks, depending on temperature, small spots appear on the leaves. As the fungus grows, the spots enlarge. The fungus in the spots may produce more spores. These spores are capable of causing secondary infections on other leaves.

In general, the leaf spot fungi are favored by cool, wet weather early in the growing season. Leaf spot diseases are seldom a problem following warm, dry weather in the spring.


Phyllosticta leaf spot of maple image by Joan Allen

All commonly grown trees and shrubs are subject to attack by one or more leaf infecting fungi. Although coniferous trees (needled evergreens) can be severely injured by leaf spot fungi, they are rarely attacked in successive years. Therefore, control measures are rarely required. Many different fungi cause a variety of symptoms on hardwood trees and shrubs. Oak, maple, sycamore, ash, walnut, hickory and horse chestnut are some trees commonly attached by the anthracnose fungi. Anthracnose is caused by several species of closely related fungi that produce brown or black lesions on leaves. Distortion of the leaves and defoliation usually result. Another leaf spot fungus will often completely defoliate susceptible hawthorns such as Paul's scarlet and English varieties by midsummer. Leaf blister of oak is common following cool, wet spring weather. Many circular raised blisters are scattered over individual leaves. Although unsightly, there is little or no damage to affected trees. Symptoms of fungal leaf spots on elms vary from small, black, pinhead lesions to brown blotches covering an extensive portion of the leaf.

As many as ten different leaf spot fungi can be found on rhododendron. Although unsightly, they rarely cause serious injury. The above are a few of the hundreds of leaf spot problems likely to be observed by the home gardener.

In many cases, the home gardener becomes overly alarmed when encountering a severe leaf spot problem. A common reaction is to run for the sprayer and quickly apply a chemical to the ailing tree. Usually this is a waste of time and money. The majority of trees and shrubs have learned to live with leaf spot diseases. Even severe defoliation will not cause the death of an otherwise healthy tree. Also, by the time symptoms of leaf spot are obvious, it is often too late to apply a chemical for control. Trees, which are subject to serious injury when attacked by a leaf spot fungus, are those trees that are under stress. This might include recently transplanted trees, trees growing under droughty conditions or trees weakened by continuous insect attack. The additional stress of a leaf spot disease on an already weak tree may cause permanent injury or death. In such cases, chemical control of leaf spots is often recommended in the spring. In order to be effective, the proper fungicide must be applied as a protectant before the fungus spore is disseminated to the leaf. Most leaf spot fungi infect trees early in the spring just as the leaves are unfolding.

Successful control usually requires two to three spray applications. In general, the first spray is applied at bud break and the second seven to fourteen days after that. A third spray might be necessary, particularly during rainy periods. The more rain the more frequent the spray applications must be. Since many of the leaf spot fungi over-winter on fallen leaves, one cultural method of reducing the severity of leaf spots is to rake and remove from your yard all old leaves under the tree. This will reduce the number of fungal spores available to infect developing leaves in the spring. Disposing of old leaves is not likely to be effective if leaves from the same species of tree or shrub in your area are not disposed because spores of most of the causal fungi can be wind disseminated for long distances.

Despite good cultural practices, pests and diseases at times may appear. Chemical control should be used only after all other methods have failed.

For fungicide and pesticide information or other questions please call toll free: 877-486-6271.


Disease Management

Leaf diseases are usually more severe on juvenile palms in a container or field nursery situation than in the landscape for two reasons. First, leaf diseases are often more prevalent on juvenile palms (palms without trunks) than on mature palms, and more likely to be debilitating to the juvenile palm if they do occur. Second, in a nursery there are hundreds or thousands of juvenile palms spaced close together, often of the same species. This allows for relatively easy movement of spores from plant to plant. Most leaf diseases in the landscape are cosmetic, since mature palms dominate, are not spaced as close together, and are composed of a variety of species. While most of the management discussion below is targeted for nurseries, the statements apply in the landscape also.

Sanitation and water management are critical for leaf spot disease management. For water management, elimination of overhead irrigation or protection from rainfall is highly recommended. Leaf spots are minimal if leaves are kept dry. If this is not possible, time the irrigation so the leaves are wet for a minimal number of hours. This usually means irrigating in the hours before dawn. Increase air circulation to keep plants drier by increasing spacing between plants and making sure larger plants are not blocking air movement to smaller plants.

For juvenile palms, it has been observed that leaf spots are more severe when the palms are grown in full sun rather than with some shade.

The nursery should be constantly monitored for leaf diseases. Prune severely diseased leaves or eliminate the palm completely. This diseased material should be destroyed or removed from the nursery as it is a source of inoculum (spores that can infect healthy leaf tissue). If mature palms are on the property, monitor them for leaf disease also. While the disease may not be debilitating to a mature palm, a mature palm with leaf disease can still act as an inoculum source.

Most leaf spot pathogens have other hosts besides palms. If the nursery produces other ornamental plants, be aware of the diseases on these plants and whether there are pathogens common between these plants and palms. Likewise, weeds may serve as other hosts for the palm pathogens.

Some of the leaf spot pathogens appear to cause disease or become problematic diseases primarily on damaged plants. Injuries may allow the fungus to become established as a saprobe (non-pathogen) on the injured tissue, followed by fungal sporulation and then infection of healthy tissue by these fungal spores. Thus, preventing injury is crucial. Monitor and control insect and rodent pests. Leaf damage or injury due to water stress, sunburn, fertilizer burn, herbicide phytotoxicity, or cold temperatures should be avoided.

It has been observed that some fungal leaf pathogens are more severe on nutritionally-stressed palms. For example, Wodyetia bifurcata (foxtail palm) suffering from iron deficiency is more susceptible to leaf spots (Figure 5). Leaf spots due to potassium deficiency create injuries that allow leaf pathogens to become established. Thus, eliminating nutrient deficiencies is the first step in managing leaf spots and leaf blights.

While fungicides may be useful to prevent further spread of the disease, they are merely a supplement to water management, sanitation, injury prevention, and good palm nutrition. Fungicides alone will not solve the problem. It is critical to understand that fungicides do not cure the leaf spots already present. Once a spot occurs, it will remain for the duration of the life of that leaf. Fungicides are used to prevent further spread of the disease by protecting leaf tissue that has not been infected by the fungal pathogens.

In the nursery situation, prune severely diseased leaves prior to fungicide application. These leaves need to be removed anyway, and this will reduce the amount of fungicide used in the process. In the landscape situation, unless the leaf spot disease is severe, leaf pruning is not recommended unless the palm is free of nutrient deficiencies. In general, nutrient deficiencies are far more debilitating to the landscape palm than leaf spot diseases.

Fungicide trials to examine efficacy of these products on juvenile palms has been conducted for specific host/pathogen groups, particularly the Helminthosporium group of fungi (Bipolaris, Exserohilum, and Phaeotrichoconis). In general, if the fungicide is efficacious against the specific pathogen on other ornamental plants, it will probably be efficacious against the pathogen on palms. Contact fungicides need to be uniformly applied to leaf tissue to protect against infection. Refer to https://edis.ifas.ufl.edu/pp154 for a list of fungicides that may be used in the landscape. Fungicides must be applied according to the label.


Development Factors

Leaf spot / melting out is one of several Helminthosporium diseases which survive in thatch during periods that are unfavorable for disease development. These fungi are most active during periods of cool (60-65°F) and wet weather, but some are able to cause disease whenever temperatures are above freezing.

Leaf spot/melting out is most severe on turf that is growing slowly due to adverse weather conditions or improper management practices. Shaded areas with little or no air movement result in weak turf and extended periods of leaf wetness that favor disease development. Deficient or excessive nitrogen, excessive thatch, extended periods of leaf wetness, drought stress, and low mowing heights are factors that encourage the development of Helminthosporium diseases. These fungi may spread to the crowns and roots and cause melting out, which is most severe during periods of hot weather.

Certain cultivars of turfgrasses are very susceptible to injury from Helminthosporium diseases while many of the newly released cultivars have exhibited good resistance.


Herbicide drift

Crops and pastures are often treated with herbicides to prevent or eliminate weeds, and drifting spray can damage tomato plants. Up to 84 percent of the cotton acreage in Texas is sprayed with broad-spectrum herbicides. They are also used on cereal and grain crops. The problem is that wind speeds as low as 5 mph can move these herbicides up to a mile.

Many home gardens are close enough to cotton and corn fields for drifting 2,4-D, dicamba, or other hormone-type herbicides to cause serious damage. Tomato plants are extremely sensitive to these herbicides: they can be injured by concentrations as low as 0.1 ppm. If only a little of the herbicide reaches the tomato plants, they can recover, but yield will definitely suffer (Fig. 8).

In addition to commercial applications, herbicides from home gardeners or their neighbors can drift onto sensitive tomatoes or other vegetables. Weed killers for lawns and landscapes often contain broad-spectrum herbicides such as glyphosate and the growth regulators such as 2,4-D and dicamba. Examples are Ortho Weed-B-Gon and Fertilome Weed FreeZone. Tomatoes are very sensitive to these herbicides even when applied at extremely low rates. Though the plants may look healthy, drift from these products can reduce the number and the quality of the fruit.

There is no remedy for leaves that are already injured by 2,4-D. If new growth continues to show injury symptoms, harvest any salvageable fruits and pull up the plants.

If new shoot growth is normal, and there is still at least 4 to 6 weeks left in the growing season, the plants may be able to outgrow the injury. New buds and leaves should begin growing within about a week. If not, pull the affected plants and replant.

To minimize herbicide drift following these steps:

  • always read and follow the herbicide label instructions
  • avoid spraying when wind speed is more than 5 mph
  • avoid spraying when wind is blowing toward sensitive crops
  • use a hooded sprayer when applying postemergence herbicides near growing plants
  • reduce spray pressure so droplet size is larger and less likely to move with the winds
  • reduce the speed of the spray application to avoid movement in the circulating air
  • ensure that the dosage applied is correct
  • use the correct spray nozzles/tips for the chemical to be applied
  • use drift reducing spray additives if available
  • wash out all previous herbicide from inside the spray tank

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