Scaffolds 99 index

DON'T BURN THE FRUIT!

For fruit growers in the northeast, pesticides are indispensable tools for controlling diseases, mites, insects, and weeds. Unfortunately, misapplied pesticides sometimes cause more damage (phytotoxicity) to the crop than would have been caused by the pests that were the target of the pesticide applications. Sometimes the causes of phytotoxicity are obvious, but in other cases the causes of the injury can be difficult to determine. An example of the latter occurred on Empire fruit in 1998.

During August and September of 1998, fruit spotting developed on Empire fruit in numerous orchards throughout the northeast. Affected fruit developed tan lesions on the sides and calyx ends of fruit. In some cases, blackened lenticels were also present, especially on the exterior of the tree canopy where fruit were most directly exposed to sprays. The injury was most severe in orchards where pesticides were applied as fairly dilute sprays (full dilute to 2X concentration). The tan lesions were especially evident where spray residue had accumulated and dripped from the lowest surface of the fruit following pesticide applications, but it was not limited to drip points. The injury occurred almost exclusively on Empire. Other varieties in adjacent rows were either unaffected or showed only minor spotting that would have escaped detection on the packing line. By contrast, some blocks of Empire were so severely affected that more than 20% of fruit were out of grade.

After extensive investigating during early September of 1998, we determined that in almost all cases, the injury seemed to be associated with captan sprays. Severity of the injury was not related to the formulation of captan (50W, 80W, or 4L). However, injury was most severe where captan was applied with foliar nutrients (especially calcium sprays) or with adjuvants that caused increased absorption of captan. Applications made at night or under slow drying conditions seemed to further increase the severity of the injury. Growers who applied captan without calcium generally had no fruit spotting.

The unusual cloudy and wet weather conditions that prevailed during the first half of the 1998 growing season may have contributed to the captan-related phytotoxicity that developed on Empire fruit. Fruit growing under stress-free conditions early in the season may have had a thinner cuticle and may have therefore been more susceptible to spray injury. We know, however, that the injury problem on Empire is more than a single-season phenomenon because similar injury had been noted for several years in western New York orchards where captan and calcium sprays were routinely applied to Empire.

Based on our experiences with phytotoxicity to Empire fruit, we recommend that growers use special care when applying summer sprays to Empire orchards. Current captan labels warn against applying captan with products that will result in increased absorption of the captan into plant tissue. That is a nebulous warning that is difficult to interpret. When multiple pesticides, nutrients, and spray additives are mixed in a spray tank, who knows if the final solution will have properties that "result in increased absorption" of captan? Obviously, it is not feasible to make separate trips through the orchard with each product that must be applied, but fruit burn caused by pesticide/nutrient sprays can also be very costly.

All we can say at this point is that combining captan and calcium in the same tank may cause phytotoxic spotting on Empire fruit. The risks are increased if the spray solution collects in drops on the bottom of fruit or if sprays are made under slow-drying conditions. We do not know if risks are dependent on the formulation of calcium that is used in foliar sprays. The role of other spray adjuvants is also unclear, but adjuvants that may contribute to increased absorption of captan sprays should be avoided.

Next in this issue: 7/6 Insects