Several disease and insect pests on apples have appeared or are about to appear. A checklist:
Apple scab . Prolonged rainy weather in the past week has resulted in infection periods for scab. If you had much scab in the orchard last year, you should begin a fungicide spray program by 1/2" green tip. If your spraying has been delayed due to the rain, you may want to consider using an eradicant fungicide such as Nova or Rubigan in order to stop infections that have already begun. If you are cooperating with ISU in using the "IRS" (Integrated Reduced Spray) schedule for scab, your first fungicide spray should go on at tight cluster.
Fire blight. Southern portions of the state have been in bloom since the weekend, and rainfall has provided another risk factor for fire blight infection. However, according to the MARYBLYT model, the average air temperature has been too cold for activity of the fire blight bacterium, so no streptomycin sprays have been recommended yet.
Cedar -apple rust. The rust galls on cedars (junipers) have begun to swell and extrude their gelatinous telial horns, which means that they can release spores soon which can infect apple, crabapple, and hawthorn. Apple growers in the vicinity of cedars, and who are growing rust-susceptible cultivars, should make certain that their fungicide sprays include materials that are effective against rust - for example, Nova, Rubigan, Bayleton, Funginex, Mancozeb, or Polyram. Benlate, Topsin-M, and Captan will not control rust.
Insects . Male codling moths have begun to emerge and are being captured in pheromone traps in central Iowa. According to procedures we are using in our on-farm IPM trials, once a total of 5 moths have been captured (biofix), an appropriate insecticide spray should be applied 250 degree-days later to control the larval stage of the insect. Commercial growers should also apply insecticide at about pink and petal fall to control tarnished plant bug and other insects that can cause dimpled, deformed fruit. DO NOT APPLY INSECTICIDES DURING BLOOM to avoid killing pollinating insects.
For additional information on IPM techniques, contact Mark Gleason (515-294-0579) or Donald Lewis (515-294-1101), or consult the new manual, "IPM for Iowa Commercial Fruit and Vegetable Growers" (PDO-83). For more information on pesticide spray options, consult Pm-1282, "Fruit Tree Spray Guide." Both are available through County Extension Offices or from Extension Distribution, Printing and Publications Building, ISU, Ames, IA 50011.
This article originally appeared in the May 5, 1993 issue, pp. 60-61.