诊断苹果树叶斑

秦冠

Infected crabapple leaf, midsummer (Esther McGinnis, NDSU)

症状

• Early season – Round, velvety, olive-green spots (less than ½ inch) form on leaves and fruit.
• Midsummer – If infection is severe, leaves will turn yellow and fall prematurely.
• Fruit – Spots turn brown and corky through time; fruit may crack and deform.

Crabapple with thinning crown due to premature defoliation (Aaron Bergdahl, N.D. 森林服务)

管理和其他重要事实

•如果可能，种植抗抗性品种. 看到“北达科他州海棠的苹果痂病管理” (PP1735).
• Raking and removing fallen leaves helps reduce the source of infection for the following season.
• Prune to allow plenty of air movement, and avoid hitting tree leaves with irrigation water.
• Many fungicides are available to prevent this disease, but the spray schedule is intensive.

Early infection of crabapple fruits (Aaron Bergdahl, N.D. 森林服务)

作者:Joseph Zeleznik和Kasia Kinzer

Yellow to orange lesions are smooth on top of the leaf (Esther McGinnis, NDSU)

The spore-producing structures are raised on the back of the leaf (Esther McGinnis, NDSU)

Cedar apple rust fruiting bodies on juniper (Terry S. Price, Georgia Forestry Commission, Bugwood.org)

症状

• Disease affects cedars, junipers, apples, and crabapples.
• Yellowish-orange lesions develop on leaves and fruit of infected apple/crabapple trees. 感染杜松的孢子在这些病变中发育.
• New infections on junipers result in small galls (or witches'-brooms) that, in moist conditions produce orange gelatinous structures that infect apple/crabapple hosts.

管理和其他重要事实

• Do not plant the juniper/cedar and apple hosts closely together because both are required for infection.
• Picking the galls or pruning the witches'-brooms off the junipers may mitigate the disease.
• Several species of this pathogen are found in North Dakota. 
• Several apple and crabapple cultivars are resistant to cedar-apple rust.

作者:Aaron Bergdahl, Joseph Zeleznik

Botryosphaeria obtusa

蛙眼叶斑具独特的紫色边缘 (Esther McGinnis, NDSU)

Yellow arrows point to frogeye leaf spot and red arrows point to apple scab (Joseph Zeleznik, NDSU)

症状

•小棕色到棕褐色, nearly circular spots with darker brown margins (frogeye leaf spot) appear on leaves.
• Dark brown, sunken cankers can form on branches and main stems. Leaves on cankered branches turn bright yellow and eventually die. 溃疡病可以缠绕和杀死树枝和茎.
•吃水果, lesions appear as reddish flecks and expand to blotches with a red halo, 然后, 棕黑交替环(黑腐病). Affected fruit can shrivel and remain attached to the tree.

蛙眼叶斑病(Aaron Bergdahl, N.D. 森林服务)

Yellowing leaves indicate a black rot canker (Joseph Zeleznik, NDSU)

Black rot symptoms on fruit (University of Georgia Plant Pathology, Bugwood.org)

管理和其他重要事实

• Remove and destroy mummified fruit and leaf debris to minimize infection the following year.
• Properly prune out infected branches and dead wood when trees are dormant. 看到“修剪树木及灌木的基本指引” (H1036).
•不建议使用杀菌剂.

作者: Kasia Kinzer和Joseph Zeleznik