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LinkedInArsenic (As)
Peach trees are very sensitive to arsenic toxicity. The disorder has been found in several peach and nectarine orchards in the San Joaquin Valley. The toxicity is often caused by past use of arsenic based pesticides and herbicides, especially where grape vineyards were previously planted. Symptoms include marginal necrosis and shotholing of basal leaves in late summer. Defoliation usually follows and the remaining terminal leaves can resemble zinc deficiency. However, upon closer examination, these leaves do not show the "little leaf" symptoms typical of zinc deficiency. Generally, young trees show more severe symptoms than older trees, probably because arsenic stays in the upper soil profile. Usually trees grow out of the disorder over time and we have observed no long term problems.
We are not sure what the mid summer leaf toxicity threshold is, but leaves with symptoms often have only 2 or 3 ppm arsenic. Arsenic is not easily leached from the soil, so no simple solutions to the problem have been discovered. In one experiment we conducted, monthly rototilling reduced the symptoms, probably because shallow roots were destroyed and thus prevented from taking up arsenic.