1995 Annual Report for ANE95-025
Toward Biotoxicant Management of Key Summer Apple Pests
Summary
Key Findings
This project developed and evaluated environmentally safer alternatives to environmentally harsh pesticides to control insect and fungal pests of apples. From mid-June to harvest, apple growers in New England and other parts of the Northeast typically annually apply three sprays of insecticide to control apple maggot flies and four sprays of fungicide to control the summer diseases flyspeck and sooty blotch.
Evaluations under field conditions have shown that a low dose of a safer and highly effective insecticide (wetable powder imidacloprid) can be combined with a particular type of latex paint to provide very long and effective residual activity of imidacloprid WP.
Many growers will be able to reduce the amount of fungicide use after early June by as much as 25 to 50 percent with the use of calcium chloride (CACL2).
Objectives
1.Evaluation in commercial orchards of odor-baited toxicant-treated spheres as a replacement for organophosphate insecticide for control of apple maggot flies, the principal fruit-damaging insect pest active after mid-June.
2.Evaluation in commercial orchards of cation salts such as calcium chloride as benign replacement for harsh fungicides for control of flyspeck and sooty blotch, principal fruit-damaging disease pests active after mid-June.
Methods and Findings
For apple maggot flies, we developed odor-baited toxicant-treated red spheres that can be used to ring perimeter apple trees in orchards. The attracted maggot flies that alight on the spheres are killed and thus prevented from injuring the fruit.
Through experimentation, we refined the composition and application of materials comprising toxicant-treated spheres to a point where we now have a specific amount and formulation of a very safe toxicant (1.5 percent active ingredient of wettable powder formulation of imidacloprid) mixed with a very effective residue-extending agent for metering out imidacloprid (Glidden latex gloss enamel paint) that will kill 90 percent of alighting apple maggot flies even after 12 weeks of field exposure under 11 inches of rainfall. The amount of imidacloprid at the sphere surface is always extremely small yet is sufficient to kill nearly all alighting flies that ingest it.
The challenge becomes one of assuring presence of sufficient fly feeding stimulant (sucrose) at the sphere surface to cause flies to feed and ingest imidacloprid (which does not kill flies unless it is ingested). We have developed two effective approaches for assuring a continuous supply of sufficient sucrose at the sphere surface, even after 12 weeks of field exposure under high rainfall.
The first approach involves placing a ring of caramelized sucrose (analogous to a "lifesaver") atop a wooden sphere coated with red latex paint containing imidacloprid. The sucrose flows down all sides of the sphere after wetting. Wooden spheres can be used year after year and annually renewed with caramelized sucrose, latex paint and imidacloprid.
The second approach involves the entire sphere body being comprised of a mixture of sucrose, flour and glycerin (which we have optimized) overlaid (after drying) by latex paint containing imidacloprid. The sucrose seeps continuously through the latex paint during and after rainfall. Sugar/flour spheres biodegrade during autumn and disappear during winter.
In 1997, 32 blocks of apple trees were ringed either with above-type odor-baited wooden pesticide-treated red spheres, above-type odor-baited sugar/flour pesticide-treated red spheres, or odor-baited wooden sticky-coated red spheres or were sprayed three times with azinphosmethyl to control apple maggot flies. Results showed sugar/flour pesticide treated spheres to be just as effective as sticky-coated spheres and both types were nearly as effective as three sprays of azinphosmethyl. Wooden pesticide-treated spheres were somewhat less effective.
However, neither type of pesticide-treated sphere can be recommended for widespread commercial orchard use until we improve upon the residual capacity of the ring of caramelized sucrose atop a wooden sphere and find ways of preventing growth of fungi on sugar/flour spheres and consumption of sugar/flour spheres by rodents and birds.
Development of fully-effective and economical odor-baited toxicant-treated spheres could substitute for all insecticide applied in New England apple orchards after early June. This would result in elimination of three sprays of azinphosmethyl (GUTHION) or phosmet (IMIDAN), whose use against apple maggot flies represents the sole need for a New England IPM orchardist to apply insecticide after early June. This will eliminate some applications of azinphosmethyl or three pounds per acre of phosmet per year. There is no current effective non-insecticidal alternative to use of odor-baited spheres for controlling apple maggot flies.
For the summer diseases flyspeck and sooty blotch, we used 1996 findings (showing that 3 orchard sprays of a 50:50 mixture of calcium chloride and captan were nearly as effective as orchard sprays of full rates of harsher fungicidal materials) as a basis for our 1997 state-wide recommendation that apple growers try this safer alternative approach to controlling these summer diseases.
With respect to fungicides, we anticipate a 100 percent reduction in the amount of benomyl, mancozeb or metiram normally used in four sprays after early June to control the summer diseases. The amount of captan normally used after early June will be reduced by 50 percent. Currently, there are no effective alternatives to the captan/calcium chloride combination tested here.
Reported December 1997.