Bloom is underway in orchards throughout Iowa (except in southernmost counties, where petal fall has occurred. With bloom comes a risk of the blossom blight phase of fire blight, a bacterial disease that is especially worrisome on susceptible varieties such as Jonathan. About 15 commercial growers (listed in a recent HHPN article) are cooperating with ISU specialists this year in on-farm trials of MARYBLYT, a computer program that advises growers when they need to spray streptomycin to control the blossom blight phase. Fortunately, the risk of fire blight has been fairly low so far this year. Despite frequent rainfall, temperatures have been a bit too low for the fire blight bacterium to become very active. MARYBLYT noted the occurrence of infection periods in three or four orchards last week, but most orchards have yet to encounter an infection period.
Flights of the first generation of codling moth should begin soon in orchards in the southern half of the state. IPM cooperators have been advised to apply insecticides on a protectant schedule through second cover, then to time additional insecticide sprays based on numbers of male codling moths captured in pheromone traps in their orchards. We recommend application of Imidan or other labeled insecticide about 7 to 10 days after capturing an average of five codling moths per trap over th course of a week. Monitoring should continue until harvest.
Bloom has begun in commercial plantings in central Iowa. This is the time to scout for tarnished plant bug, or TPB. TPB nymphs can be counted by tapping blooming clusters lightly against a white pan, then counting the green, flightless nymphs as they scurry around the pan. We recommend scouting at least half a dozen locations in the field, and tapping a total of 30 clusters per field. If the average count of TPB nymphs equals or exceeds 0.5 per cluster, application of an insecticide is advisable. Thiodan is the product of choice; malathion is less effective, and Sevin is ineffective. If you apply insecticide during the bloom period, take care to do it in the late evening, after bee activity has ceased, in order to avoid killing your pollinators.
This article originally appeared in the May 19, 1995 issue, p. 72.