Chestnut mining moth - prevention and control methods
Among the pests, fully enjoying the climate change, not a single insect has spread as widely as the chestnut mining moth. In recent years, it has been causing a lot of trouble in urban landscaping, and the owners of private gardens. After all, compact varieties of horse chestnuts are becoming more and more popular in the design of large areas, and the maples and girl's grapes loved by the Ohrid miner do not lose their leadership positions at all. You can fight chestnut moth, but the loss of decorative plants can not be avoided even with timely control measures. And this is far from an easy process.
What harm does the chestnut mining moth do?
Chestnut Mining Moth (Cameraria ohridella), Ohrid miner, chestnut miner - the main pest of horse chestnuts with an extremely fast pace of distribution, a variety of butterflies of the category of moths.
Caterpillars "mine" the leaves from the inside and lead to their premature death and decay, weakening the tree and causing a catastrophic loss of decorativeness and endurance, resulting in frost damage, other pests and diseases.
The chestnut miner activates and first appears on chestnuts even before the mass blooming of leaves, when the petals on the flowers begin to open. Usually Ohrid miner is active for two seasons in a row. Infection of trees this year is almost a guarantee that next spring the area of damage will be even larger.
But many scientists note that after the peak of activity for several years, the pests almost disappear, presumably going to new territories.
The massive shedding of sluggish, lifeless leaves by chestnuts in July and August, which is so often seen in cities in recent years, is the result of the defeat by the Ohrid miner. The main symptom is leaf wilting. Hundreds of yellow or reddish traces appear on their surface - “mines” (up to 700), which leave caterpillars in the epidermal layer, feeding on juices and cells.
Leaves die off quickly, lesions grow more and more, green areas completely disappear. It is very difficult to diagnose an infection - the spots resemble both rust and fungal infections. Recognizing the "work" of miners inside the leaves is possible only by the absence of a thin yellow border and black spots-bubbles (pycnids) on mines. And, of course, for accelerated leaf fall.
Chestnut mining moth causes trees so irreparable harm that most of the decorative planting of horse chestnuts is in danger of death:
- Due to the rapid loss of green mass, chestnuts do not accumulate nutrients and cannot properly prepare for wintering, most often they partially freeze out even in mild winters.
- The trees partially dry and release new leaves very slowly.
- Endurance suffers - weakened chestnuts become defenseless against leaf-eating pests and affecting shoots and trunks. Mushroom diseases spread to them ten times faster.
- Decorative chestnuts, even with a primary lesion, lose completely. If in private gardens you can fight to save them, then in urban landscaping with critical aesthetics, mature trees almost always require replacement and immediate preventative measures.
Without measures to stop the spread of the pest and treatment, trees affected by the Ohrid miner can die in a few years.
What does a chestnut mining moth look like?
The Ohrid miner was first recorded only 30 years ago in Macedonia, then this pest was considered a relict Balkan species. From a small range in Greece and the Balkan Peninsula, this moth has captured all of Europe and is actively moving to the East.
Regardless of theories of origin and whether the Ohrid miner was imported from East Asia and North America or is originally European, due to catastrophic climate change, pests once found only in the south have spread even in Scandinavia.
The Ohrid miner is a small butterfly with a body length of up to 7 mm and a wingspan of up to 10 mm. This mole miner has a very decorative motley pattern on the reddish front wings and black dots on the legs.
One female chestnut mining moth can lay more than 80 eggs. Butterfly eggs are so tiny that it is almost impossible to notice them with the naked eye. They are scattered on the front side of the leaf, near the veins.
Caterpillars pass 6 ages with a radically different form of nutrition and lifestyle. They are also hardly noticeable: their size varies from less than 1 mm at the beginning of development to a little more than 2 mm in the third stage and the “final” 5-6 mm.
Caterpillars do the most harm in the first five phases - from feeding only the plant sap to switching to eating the chestnut leaf tissue itself. Only at the age of six do they start spinning and pupation. Pupae of a chestnut mining moth do not exceed 0.5 cm in length.
This is the most aggressive of all types of mining moths. For the entire embryonic period, this butterfly has enough from 4 days to 3 weeks. The development of a caterpillar takes no more than 45 days in the most adverse conditions. Ohrid miners can produce three offspring in one season during the warmer months. And no other pest destroys the foliage of ornamental trees so quickly as the Ohrid miner.
Plants affected by the chestnut miner
Despite its name, the chestnut mining moth affects not only chestnuts, but not all horse chestnuts are distributed equally.
The Ohrid miner is the main pest of white-flowering horse chestnuts, in particular, ordinary and Japanese. Compact hybrids suffer greatly from it, the degree of stability of which varies depending on the conditions and characteristics of the selection.
Individual varieties of horse chestnut are unattractive or even fatal to this type of butterfly. So, on horse chestnuts Chinese, California, meat-red, Indian, Assamese, small-flowered caterpillars die in the early stages of development.
Choosing the right species and checking the resistance to Ohrid miner for a particular plant when buying is the best solution. Indeed, vulnerable varieties and species have more and more stable competitors every year.
In addition to chestnuts, the Ohrid miner is also found on several decorative types of trees and vines:
- five-leaf girl’s grapes;
- decorative maples, especially white and holly.
Chestnut Mine Control Methods
In the fight against chestnut mining moths, prevention is the most important means of control and the key to the success of any event. Quickly cleaning and destroying the leaves of affected trees is critical. They help reduce the distribution of chestnut minerals and hunting belts.
One of the most effective strategies for combating this type of moth both globally and in your garden is to use biological methods, including fungi and predator insects that can control populations of Ohrid mineral.
To create an environment that is most unfavorable for a chestnut mining moth, it is better to combine several simple but effective methods:
- Attracting singing and healthy birds, including tits, starlings and sparrows to the garden - hanging feeders and birdhouses.
- "Launch" of ladybugs, riders, in particular trichograms and other beneficial insects.
- Installation in the garden of "hotels for insects" in order to attract the natural enemies of the moth-mineral.
Read more about houses for healthy insects in our material. Hotel for beetles - a garden house for healthy insects.
The main way to deal with chestnut mining moths is the treatment with systemic insecticides of hazard class 1 and 2. In particular, based on pyrethrum, deltamethrin, diflubenzurol, chitin synthesis inhibitors, the systemic insecticides Insegar, Lufox, Confidor, Actellik, Iskra, Imidacloprid. Or - an alternative to it, but very expensive treatment with special bioinsecticides of a narrow specialization of fungal origin. So far, it is available only in some botanical gardens (for example, the drug ‘Revive’).
When choosing a drug, it is enough to make sure that there are mining moths in the list of species and manufacturer's recommendations. The methods of using insecticides are limited due to the specifics of the development of chestnut minerals: spraying for this moth living in the thickness of the sheet is ineffective, because it is impossible to spray huge crowns uniformly and safely.
The only options for plant protection are:
- trunk injection;
- less productive application of insecticides in the soil.
The annual treatment with insecticides can be carried out only in May or June (when the temperature rises to 20 degrees) at the beginning of leaf blooming. With severe damage to chestnuts, insecticides must be combined with systemic fungicides to compensate for the loss of resistance to trees and protection against fungal infections.
Chemical methods of control are associated with considerable risks: it is necessary to evaluate the effect of systemic pesticides on the ecosystem, the danger to humans, the use of the area around the tree, and the effect on neighboring plants and honey insects, in particular bees.
Used to combat chestnut mining moths and pheromone traps or spray preparations, but they are still inaccessible.