Walnut diseases and pestsare threats that, unfortunately, are not uncommon. Infected walnuts can become ill for many years and bear less fruit. Therefore, it is important to learn what diseases and pests threaten walnuts and how to properly recognize them and further treat them. Find out in the article below, where we've outlined the most commondiseases and pests of walnut
Walnut diseases - anthracnose
Walnut diseases
Walnut anthracnose- this is the most dangerous diseasewalnut diseaseTrees are particularly sensitive to it in rainy summers. Anthracnose is caused by the fungus Gnomonia leptostyla. The pathogen hibernates in fallen leaves, which are a source of spores in the spring. Most often, leaves or fruits become infected when there are drops of dew or rain on their surface. Symptoms mainly appear on leaves, shoots and fruits.The leaves initially show yellow spots that gradually darken. The spots are quite large, angular and arranged between the veins. They often blend together, mainly covering the edges of the leaf tissue. In the final stage, the leaf tissue covered with the blot turns brown and dries up. On the underside of the leaf, brown-black, concentrically arranged fruiting bodies appear on the surface of the spots. The most affected leaves fall.
There are also brown spots, slightly recessed, on the green layers of the fruit. Stains often cluster more strongly on one side.Early fruit buds affected by the fungus simply rot, while those that were infected at a later stage of development do not mature and fall prematurely. Brown-black fruiting bodies also appear on spots on the green crust. Green, unripe parts of the shoots are also infected and brown spots appear on them. Heavily infected shoots dry out, and those that have started to lignify have cracked bark in the place of the spots.
Combating walnut anthracnoseis done with fungicides before and after flowering. We start spraying at the beginning of May, as soon as the first developed leaves appear, using the Miedzian 50 WP preparation, because it simultaneously fights another walnut disease - bacterial blotch. Subsequent treatments at intervals of 10-14 days are performed with Dithane NeoTec 75 WG, repeated 2-3 times.Another recommended fungicide is Signum 33 WG. We can use it from the beginning of the flowering phase to the end of the development phase of the walnut fruit, making two sprayings with an interval of 14 days.Raking and removing fallen leaves and fruit is also mandatory.
Note!
Until recently, it was common practice to burn plant debris infected by diseases or pests. However, according to the current regulations, smoking leaves and branches, even if they come from sick plants, is forbidden. From gardens and plots, we should dispose of them in accordance with the principles of segregation and waste return in force in our commune. Cut branches and removed leaves are called green waste.
Bacterial gangrene of walnut- this disease of the walnut is caused by the bacterium Xanthomonas campestris pv. juglandis. Often this disease is also calledWalnut bacterial blotchThe symptoms are similar to those of anthracnose. The spots are brown-black, they merge into clusters, with the difference that they are smaller. They appear on leaves and petioles. The spots on the fruit are also numerous, brown-black and recessed.The spots on the shoots have the shape of light streaks, darkening later. Heavily infected shoots die. Fighting thiswalnut diseaseinvolves cutting out and removing affected shoots. The tree should be sprayed with copper fungicides every 10-14 days from May to the end of June. Miedzian 50 WG is the best here.
The disease of vaccinated walnuts- is an extremely dangerous disease of walnuts, both vaccinated in the ground and in a greenhouse or foil tunnels. At the site of vaccination, tissue darkening is visible, extending to the tissues of the scions. A sooty bloom appears on the scions and rootstocks. In the final stage of the disease, the scions stop developing and die. The disease is caused by the fungus Chalaropis thielavioides. Fighting is difficult. Protection is mainly based on the collection of he althy starting material for vaccination. When symptoms appear after vaccination, there is little that can be done. That is why it is so important to prepare the right material for grafting.As a preventive measure, rootstocks and slips can be sprayed with Kaptan 50 WP at a concentration of 0.2%. Also, cleanliness in the vaccination room and where the vaccinated nuts will be stored.
Powdery mildew of walnut- usually occurs in warm and humid summers. Most often, the fungus infects young trees, and does not cause major losses in older specimens. The disease is caused by the fungus Phyllactinia corylea. It mainly affects leaves and young shoots. The symptom is a white, cobweb-like bloom. The growth of young, infected leaves is inhibited. The presence of powdery mildew weakens the growth of trees and lowers their resistance to low winter temperatures. Ecological control consists in cutting the infected shoots and leaves with pruning shears. In case of severe infection, you can use fungicides: Dithane NeoTec 75 WG or Miedzian 50 WG.
Walnut pests
Walnut specula(Aceria tristriatus) - it is an arachnid invisible to the naked eye - a mite that sucks sap from leaves.Thiswalnut pestfeeds on the underside of the leaves, producing lighter patches. The massive appearance of the pest causes the leaves to twist and fall, and the growth of trees is impaired. Spells hibernate in buds. In the fight against thiswalnut pest , first of all, remove infected leaves. The following acaricides can be used for spraying: Magus 200 SC, Sumo 10 EC, Zoom 110 EC.
Ornamental aphids nut(Chromaphis juglandicola) - aphids on the walnut are quite rare, and if they do appear, their range is small. They feed on leaves and petioles. The larger walnut ornament inhabits the upper surface of the leaf, preferably along the main nerve. The aphids are yellow-green, 3 mm in size. The smaller walnut ornament is half the size and occupies only the lower side of the leaf. In garden centers, we can find a wide range of agents to combat aphids, including Decis 2.5 EC and Pirimor 500 WG.
In addition, walnuts can be attacked byleaf-eating caterpillars ,spider mitesorplum cupThey are also threatened by soil pests such as the May beetle grubs or wireworms - the larvae of some beetles and marsh beetles. These pests feed on young walnut roots, and also gnaw the bark from large roots. This results in weaker growth and yielding, and in extreme cases may lead to tree dieback.
We should also remember that walnuts are also our delicacy, but also squirrels, donuts, nuts, jays, and even crows and rooks. However, if we only know how to divide, and our walnut cultivation is not geared towards sales volumes, we should not have too much loss because of these animals.
Katarzyna Matuszak
