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Fruit Trees Damageed by April Freeze What to do Now

Posted by Paul Mariman -

For growers whose orchards suffered or total or near-total crop loss in the freezes about 4 weeks ago, tree management, disease management, and insect management should be modified to reduce some expenses usually needed to bring marketable fruit to harvest. Here are few considerations ...

Caring for Trees that Lost Their Crop due to the April 11-12 Freeze

Damage from the April 11 and 12 freeze is extensive in some areas and not yet fully assessed. Perhaps the most significant impact of this cold wave is on the tree fruit industry throughout the Midwest and North East, because trees were either in bloom or already had small size fruits. Damage to the apple crop is more severe in the central and northern counties of Illinois. Some growers in central and northern counties are reporting near complete loss of fruits on most varieties, including Honeycrisp, Goldens, and Jonathans. Damage to peaches in western Illinois was very light, except on trees in poorly air-drained areas. In addition to damage to fruits, leaves were also damaged. Some leaves lost a sizable portion of their surfaces, while others were completely killed, especially on grapes.

Many growers are asking how to manage trees that have lost their crop and have damage to their leaves. Unfortunately, many fruit growers think that because the trees have no crop, it automatically means that they are going to grow vigorously, and so they tend to neglect them. Freeze damage does not affect the fruits only, it does affect the leaves and it also impacts the reserve carbohydrates if the damage occurs after fruit set. Damaged trees, especially among stone fruits, should be examined carefully for signs of leaf yellowing and treated accordingly. In apples, a dose of boron and other micronutrients such as zinc and manganese will help improve leaf efficiency and return bloom. A cup of balanced fertilizer will help apple trees with leaf damage. Avoid treating young trees with boron.

Mosbah Kushad (217-244-5691; kushad@illinois.edu)

Fungicide Programs for Freeze-Damaged Apple and Peach Orchards

Apple and stone fruit crops are good in southern and western Illinois; there are some losses in northern Illinois, and the heaviest damage occurred in the east-central part of the state. Where a partial crop will still be marketed, even a light crop needs to be protected by a "normal" spray program, and registered fungicides are listed in the 2012 Commercial Tree Fruit Spray Guide (http://www.hort.purdue.edu/fruitveg/2012ID168.pdf). For the orchards that have no crop, growers should focus on minimizing development of scab and powdery mildew on apples and powdery mildew and bacterial spot on peaches. The best approach is to scout each orchard and apply controls as needed.

Apples. Two major diseases that develop in spring in apple orchards in Illinois are scab and rust. Powdery mildew has been observed in some orchards, but it has not been a serious issue. Where primary scab was effectively controlled, no additional fungicide sprays may be necessary, except for cultivars that are highly susceptible to mildew. Also, rust diseases are controlled when scab is effectively managed.

Where scab lesions are present in trees with no crop and there is no need for mildew control, a single application of Captan at the maximum label rate in late May to mid-June will limit secondary spread of scab to new leaves. Secondary spread of scab in summer is often limited by hot weather. Temperatures above 85°F significantly reduce viability of conidia. However, if the weather stays cool and wet, further applications of Captan may be needed during June and July to slow secondary spread of scab, especially in vigorous trees where shoot growth may continue unabated. Where considerable leaf scab is evident in late summer, a fungicide spray in September can help to limit the spread of scab to the undersides of leaves during autumn. Preventing spread of scab during autumn can significantly reduce the amount of carry-over inoculum for next year. There is no need for 100% control of scab in an orchard with no crop, so long as the foliage remains reasonably healthy, it will be more cost-effective to control scab next year.

Apple trees also can tolerate some powdery mildew, so 100% mildew control is not essential. Nevertheless, for mildew-susceptible cultivars such as Ginger Gold, Cortland, Paula Red, and Rome, mildew sprays may be needed during summer to limit the amount of carry-over inoculum for next year. Sulfur is the cheapest fungicide for mildew control, and it should provide adequate protection for trees with no crop. Sulfur is easily removed by rain. Mildew-susceptible apple cultivars should be sprayed with sulfur at about 14-day intervals or after rains of one inch or more.

Peaches. Some peach orchards in central Illinois have lost their entire crops. Disease control may not be necessary in peach orchards with no crop. Control of powdery mildew and bacterial spots of leaves, however, may require fungicide applications. Powdery mildew could rapidly develop in susceptible cultivars, and spray treatments may be needed. Application of sulfur [e.g., Microthiol Disperss (80% sulfur) at 10 to 15 lb/A], at 14-day intervals, can control powdery mildew. Spray the trees as needed. Bacterial spot of peach is a serious disease in Illinois and will develop on leaves in moist conditions. Severe bacterial spot causes defoliation in susceptible varieties. If needed, the trees can be sprayed with copper at the rate of 0.25 - 0.50 lb copper per acre.

Mohammad Babadoost (217-333-1523; babadoos@illinois.edu)



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