Codling moth. Pheromone trap captures continue to show great variation from orchard to orchard. While the average number of male moths captured in most orchards has been below or just slightly above the spray threshold of 5 moths per trap, a few orchards have had much higher numbers. What is different about these orchards that causes such high populations? One factor may be the way in which culled fruit are handled. The orchards with the high moth populations had large accumulations of 1992 culls in or near the orchard, either in piles or on the orchard floor. Large numbers of cull fruit can provide an overwintering refuge for codling moth, which may then emerge to attack the next spring's apple crop. The take-home message is: Keeping the orchard and its surroundings as free as possible of cull apples (as well as untreated or abandoned apple trees) can help to lessen the risk of severe codling moth problems.
Leather rot. This disease, caused by the soilborne fungus Phytophthora cactorum, has devastated some strawberry plantings during the last few weeks. The pathogen is splash-dispersed, meaning that our abundant rainfall picks up contaminated soil particles and splashes them onto berries, which are then invaded by the fungus. A leather rot epidemic is not only a depressing sight, it smells bad, too. Immature infected berries develop hard, brown spots, and ripening berries take on an unnatural purple discoloration and a smell that is reminiscent of motor oil. The taste of a leather rot-infected berry is uniquely disgusting - adjectives such as "bitter" and "acrid" hardly begin to describe it - and is a hard-to-forget experience, especially for customers.
The most important thing to remember about leather rot is that significant losses can be avoided on most Iowa soils by following one basic practice: mulching. If the planting has been well mulched the previous fall or sometime before the bloom period with straw, chopped cornstalks, etc., so that the berries can't be splashed with soil particles, leather rot damage is usually negligible. If mulching is inadequate, or the soil is so heavy that standing water persists in the field for long periods after rainfall, leather rot can lay waste to the planting, causing over 80% fruit infection in some cases. Yes, it's a nasty disease... but you can virtually prevent it by mulching. The systemic fungicide Ridomil can be applied once before the plants start growth and again at fruit set to suppress the leather rot fungus, but in a wet year such as 1993 it will not be effective unless adequate mulching has been done.
This article originally appeared in the June 30, 1993 issue, p. 109.