David Doll2 CommentsJuly 20, 2009Nutrient

Potassium thiosulfate toxicity on almond

During periods of high heat and the corresponding high evapo-transpiration, several unique orchard problems can occur. Most of these are due to fertigation methods which have been widely adopted to increase fertilizer application efficiency. The benefits of fertigation greatly outweigh most negative impacts, but caution must be used as a simple mis-calculation can cause orchard damage. A field call from a grower in late June demonstrated the potential problems that can occur with fertigation. Observations of yellowing leaves, leaf drop, and death of lower limbs raised concerns by the grower and pest control advisor (PCA), prompting an orchard visit. Initial Observations: Upon arriving to the 11th leaf Sonorra/Nonpareil/Carmel (all on Nemaguard) orchard I noticed excessive leaf drop across all varieties (Picture 1). Most of these leaves were coming from the interior of the canopy, suggesting the possibility of drought stress from improper irrigation scheduling. Lower leaves found on the interior of the canopy were burnt back, with a crispy texture. Leaves closest to the trunk that were completely yellow were beginning to abscise, while leaves on the tips of the branches remained green (Picture 2). This is in contrast to lower limb dieback, which causes soft yellow leaves found on the ends of interior branches. Picture 1: Leaf drop associated with the over-application of potassium thiosulfate. Picture 2: Leaf wilting and “dieback” associated with the over-application of potassium thiosulfate. Note how the interior branches are more affected than the branches on the outside edge of the canopy. Up-Close Observations: Close inspection of the leaves revealed a necrotic tip, or burnt region of the leaf. This leaf was surrounded by a yellow halo (Picture 3). Typically, a yellow halo around a necrotic area would suggest the possibility of almond leaf scorch, but due to the widespread occurrence of the problem, this

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David Doll1 CommentJune 9, 2009Weeds

Herbicide drift damage to a Butte/Padre almond orchard by 2,4-D

May is the time of the year for the herbicide injury to almonds. High winds, fast growing weeds, and too many orchard tasks to complete in a day are the typical causes of herbicide drift. Herbicide drift can be prevented by following a few simple principles:1). Avoid windy days when applying herbicides,2). Apply the correct herbicide that targets the correct weed,3). and apply the herbicide at the proper rate. A field call in mid-May by a grower yielded a case of typical 2,4-D injury to almond. The 2nd leaf orchard was 50% Butte and 50% Padre on nemaguard rootstock. The orchard was situated in sandy soil with microsprinklers used for irrigation. The grower reported multiple trees showing dieback of new growth. He was uncertain of the cause and thought verticillium wilt may be affecting his orchard. Picture 1 shows the overall symptoms of an affected almond tree. Picture 1: Overall tree symptoms caused by 2,4-D herbicide drift. Note tip dieback and odd growth. Overall, the distribution of the symptoms were found throughout a large percentage of the block. Many trees where showing a “shepherd’s crook” of the new growth indicating either a wilt disease or herbicide/salt issue. Picture 2 shows the severity of the symptoms on the new growth of the almond tree. Picture 2: Branch tip dieback due to 2,4-D herbicide drift. Leaves at the tip of the crook were crispy, indicating a fast wilt. Shoots with contorted growth were found throughout the canopy. Pictures 3 and 4 are of these symptoms. Picture 3: Branch damage from 2,4-D herbicide drift. Branch is showing the “shepherd’s crook” symptom, typical of vascular wilt pathogens or salt/chemical damage. Picture 4: Contorted growth of new growth caused by exposure to 2,4-D herbicide. With the exception of the contorted growth, symtpoms expressed by the

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David Doll1 CommentJune 4, 2009Nutrient

Zinc Deficiency in Almond

A farm call in early April yielded a problem that proved to be difficult to diagnose due to complicating factors. The orchard was three years old with three varieties planted on nemaguard rootstock: 50% Nonpareil, and two pollinators Monterrey (25%) and Avalon (25%). The soil was loamy sand to sand, very coarse, and a hardpan was present. Tree sites were backhoed before planting to remove the hardpan within the tree site. The previous cropping cycle was almond, but methyl bromide was used to fumigate the soil to kill nematodes, soil pathogens, and weeds. Irrigation is by moveable sprinklers. Initial Observations:Overall the orchard has variable growth overall. Some trees are large, some trees are smaller. Branches in the top of the tree have sparse growth. This growth, however, seems to be limited to one variety – the nonpareil. The symptoms are therefore found in every other row. Photo 1 shows the symptoms of sparse growth in the upper trees of one row. Photo 1: Overview of the orchard showing symptoms. Note that the symptoms are more severe on one row of trees. Up-Close Observations:Sparse tree growth has tufts f leaves that are “bootstrapped.” Leaves are deformed are have not completely formed physiologically. Photos 2 shows a symptomatic tree and photo 3 shows a close up of effected leaves. Photo 2: An individual tree showing symptoms of poor leaf growth and development. Photo 3: An isolated branch showing “bootstrapped” leaves. Possible causes:Glyphosate (Herbicide) damage (Round-up)Dormant applications of chloropyrifos (insecticide) (Lorsban)Zinc Deficiency Diagnosing:The applications of chloropyrifos, a broad spectrum insecticide, can sometimes lead to similar growth responses in almond when applied in the delayed dormant stage. Questioning of the grower yielded that no chloropyrifos was used within the orchard – in fact, he doesn’t use chloropyrifos in any of his orchards. Good –

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