MSU Extension Chestnuts

Weekly weather review

Temperatures over the last 30 days were near average across the state. In terms of precipitation, the east central and southeast Lower Peninsula received above average precipitation while north and western Michigan was below average. Drought conditions persist across much of Michigan, although recent precipitation should help alleviate dry conditions.

Looking ahead

NOAAs 6-10 day outlook suggests near normal temperatures and precipitation.

View the most recent MSU agriculture weather forecast.

Management activities

Fertility

July is a great time to test tissue for nutrients. In recent years, some growers have also been utilizing tissue nutrient testing as another data point for making nutrient adjustments. Sampling chestnut leaf tissue for analysis is similar to protocol in other crops, with a few important caveats.

Collect samples from this year’s new growth before vegetative terminal growth stops for the year. Terminal growth typically stops in early August as the trees start developing burs.

Collect five to 10 leaves per tree from multiple terminal branches. Sample along the length of the new growth.

Carefully read the protocol from the testing facility you plan to utilize to ensure you receive a valid report.

There are many labs that provide leaf analysis testing, a few are listed here for your convenience:

A & L Great Lakes Laboratories in Fort Wayne, Indiana (phone: 260-483-4759)

Brookside Labs in New Knoxville, Ohio (phone: 419-753-2448)

For more information on the general protocol for nutrient sampling, refer to the Michigan State University Extension article, “Time to collect leaf samples for nutrient analysis.”

Michigan State University Extension is requesting tissue testing results from this season or previous years be shared via this survey.

We are now past the window for granular fertilizer applications. For nutrient management considerations, please reference the 2023 Michigan Chestnut Management Guide or the Nutrient Management section of the MSU Extension Chestnut website. To receive nutrient management recommendations from MSU, pick up a commercial test at your local Extension office.

Insect pests

Growers should be scouting for chestnut weevil as kernels develop. The lesser chestnut weevil (Curculio sayi) is an important pest of chestnut in Michigan. Lesser chestnut weevil is native to North America and host-specific, only infesting tree species in the genus Castanea (American chestnut, Chinese chestnut, European chestnut and chinquapin). Lesser chestnut weevil lay eggs on developing kernels and the resulting larvae feed on and damage the kernel making them unmarketable. Even worse, larvae present in nuts at harvest can result in “wormy” nuts making their way to consumers. Over the last decade, Michigan chestnut producers have observed an overall increase in the number of lesser chestnut weevil larvae in nuts at harvest, particularly in southern Michigan. The highest lesser chestnut weevil infestation levels are observed in years with lower yields.

Lesser chestnut weevil have robust bodies, long snouts and are dark brown or tan with brown mottling or stripes. Lesser chestnut weevil are 0.25 inch in length, with a snout of equal or greater length. In Michigan, a small number of adult lesser chestnut weevil begin to emerge in June-July as catkins form but based on trapping data, most of the adult activity occurs in September and October as burrs develop and mature. During September and October, adult weevils mate in the chestnut canopy and females then lay eggs in the kernels. Eggs hatch in one to two weeks and the larvae begin feeding inside the kernels. The larvae feed inside the kernel for three to five weeks before exiting the nuts, dropping to the orchard floor and burrowing into the soil. The larvae remain in the soil for one to three years before pupating and emerging as adults.

Scouting for adult weevils should begin just before catkin bloom and continue regularly until harvest using visual observation and limb-tapping. To use the limb-tapping technique, place a light-colored sheet under the limb you are sampling and tap the branch with a padded pole or stick (gently to avoid damage to the tree). Jarring the branch causes the weevils to drop from the tree onto the sheet. Weevils will “play dead” when disturbed, so don’t be fooled. Chestnut weevils are substantial in size and should be visible if present. Be sure to limb-tap tree on both the edges and interior of orchards as well as any known hotspots.

There are two primary goals in the management of chestnut weevil, to prevent weevil larvae in nuts at harvest and to prevent kernel damage from activity during kernel development. The most critical control period includes the five weeks prior to harvest as eggs laid during that timeframe can result in larvae in the nuts at harvest. However, to limit quality and yield issues growers need to protect developing kernels from the time burrs begin to swell through harvest.

Orchards with known lesser chestnut weevil infestations should plan to utilize insecticides to target the later windows of potential adult activity that coincides with kernel development through harvest. Protecting developing burrs prevents egg laying and larval damage to kernels. Growers are advised to observe burr development and scout for weevil to accurately time insecticide applications. In Michigan, the insecticide treatment window will generally start in early August and extend through harvest in September or October. Precise insecticide timing is dependent on location and chestnut species or cultivars. Insecticides should not be applied during adult activity in May-June as bees are often foraging in the orchard at this time.

Growers should consider a number of factors when selecting insecticides for weevil control, including relative efficacy against other relevant pests like Japanese beetle, European rose chafer and leafhopper, known weevil efficacy in other crops, toxicity to beneficials, mode of action, preharvest interval, resistance management, and the number of applications allowed per season. The goal of insecticide applications is to kill adult weevils when kernel development has begun and before egg laying occurs.

The table below includes four candidates for chestnut weevil management in Michigan based on the selection criteria previously described. Growers should be using a minimum of two modes of action in rotation to prevent resistance development. Using pyrethroids may also be considered and the preharvest interval of all materials should be considered. Pyrethroid use in early-mid growing season is not recommended as it can result in increased pest mite populations. For a complete list of registered pesticides, visit www.chestnuts.msu.edu for the latest Michigan Chestnut Management Guide.

Asian chestnut gall wasp emergence continues in infested orchards. Effective pest management starts with active scouting. Chestnut growers in counties west of Highway 127, especially areas south of I-96 in lower Michigan, should be scouting their trees for evidence of Asian chestnut gall wasp during the growing season and again in fall or winter, after leaf drop.

In late spring and summer, green or reddish galls can be observed on branches or leaves. In fall and winter, look for dried, brown galls on the shoots. Many old galls remain on the tree through winter and are more visible after leaves drop in fall. These old galls can remain attached to the trees for at least one or two years after the wasps have emerged.

Growers with young trees should carefully monitor for Asian chestnut gall wasp adult flight and consider applying a pyrethroid insecticide for control. Young trees are particularly susceptible to severe damage by Asian chestnut gall wasp due to the limited number of buds and the need to establish tree structure during the first years of establishment. Growers can hang yellow sticky traps in mid-late June in the canopy to passively trap for adult flight and better time pesticide applications. Growers with mature trees should monitor the impact of Asian chestnut gall wasp on yield and tree health and make management decisions accordingly.

For more information, check out the Asian Chestnut Gall Wasp bulletin.

Japanese beetles are active. Japanese beetle adults are considered a generalist pest and affect many crops found on or near grassy areas, particularly irrigated turf. Adult Japanese beetle emerges around early July and feeds on hundreds of different plant species, skeletonizing the tissue. If populations are high, they can remove all of the green leaf material from the plants.

There are no established treatment thresholds or data on how much JB damage a healthy chestnut tree can sustain, but growers should consider that well-established and vigorous orchards will likely not require 100% protection.  Younger orchards with limited leaf area will need to be managed more aggressively.

For more information on Japanese beetle, check out the pest management section of the chestnut webpage.

Potato leafhopper numbers have remained relatively low in most locations but should continue to be monitored. Like many plants, chestnuts are sensitive to the saliva of potato leafhopper, which is injected by the insect while feeding. Damage to leaf tissue can cause reduced photosynthesis, which can impact production and quality and damage the tree. Most injury occurs on new tissue on shoot terminals with potato leafhopper feeding near the edges of the leaves using piercing-sucking mouthparts. Symptoms of feeding appear as whitish dots arranged in triangular shapes near the edges. Heavily damaged leaves are cupped with brown and yellowed edges and eventually drop from the tree. Severely infested shoots produce small, bunched leaves with reduced photosynthetic capacity.

Adult leafhoppers are pale to bright green and about 1/8 inch long.  Adults are easily noticeable, jumping, flying or running when agitated. The nymphs (immature leafhoppers) are pale green and have no wings but are very similar in form to the adults. Potato leafhopper move in all directions when disturbed, unlike some leafhoppers which have a distinct pattern of movement. The potato leafhopper can’t survive Michigan’s winter and survives in the Gulf States until adults migrate north in the spring on storm systems.

Scouting should be performed weekly as soon as leaf tissue is present to ensure early detection and prevent injury. More frequent spot checks should be done following rainstorms which carry the first populations north. For every acre of orchard, select 5 trees to examine and inspect the leaves on 3 shoots per tree (15 shoots per acre). The easiest way to observe potato leafhopper is by flipping the shoots or leaves over and looking for adults and nymphs on the underside of leaves. Pay special attention to succulent new leaves on the terminals of branches.

For more information on insecticides available for the treatment of potato leafhopper refer to the 2023 Michigan Chestnut Management Guide.

European red mite populations have been higher than typical. At this point in the season, scout for eggs, immatures and adults on upper leaf surfaces, particularly leaves on the vigorous and upright water sprout branches found in the interior canopy of established trees. European red mite seem to prefer branches with excessive growth rates. Adult European red mite are red and have hairs that give them a spikey appearance. Adult and nymph feeding occurs primarily on the upper surface of the leaves. Summer generations, favored by the hot and dry weather, are able to complete their life cycles much faster with as little as 10 days between generations under ideal conditions making vigilant monitoring critical at this time.

As you scout, remember that not all mites are bad. Consider documenting the levels of predacious mites in your orchard. If healthy populations of mite predators exist, they will continue to feed on plant parasitic eggs and nymphs and can be an effective component of your mite management program. Predaceous mites are smaller than adult European red mite and twospotted spider mite, but they can be seen with a hand lens and typically move very quickly across leaf surfaces.

Mite control starts with monitoring early in the spring looking for the overwintering eggs (European red mite) and assessing the mite pressure. Ideally, growers will be using limited insecticides with miticidal activity in their season long programs, as that protects their beneficial mite populations which help minimize pest mites. If pest mite populations are high enough to require control, superior oil application when the trees are dormant is an effective method of treatment. If issues with mites arise during the growing season, refer to the Michigan Chestnut Management Guide for control options.

Disease

Existing chestnut blight infections (caused by Cryphonectria parasitica) can be observed. There are no commercially available treatments for chestnut blight. Growers may prune out infected branches or cull whole trees as needed to limit disease pressure. Infested material should be burned or buried to further limit inoculum spread. To learn more about chestnut blight, visit the pest management section of the chestnut webpage.

During the 2022 growing season, the causal agent of oak wilt (Bretziella fagacearum) was cultured out of a chestnut tree in an orchard with multiple, established chestnut trees exhibiting symptoms of wilt and dying. As leaves expand in orchards around the state, growers may see trees with wilt-like symptoms. While there are many causes of wilt symptoms in chestnuts (drought, winter injury, phytophthora, armillaria, chestnut blight), consider the possibility of oak wilt as well. To learn more about this issue, refer to the MSU Extension article, "MSU investigating oak wilt as the cause of sudden chestnut tree decline."

Stay connected

For more information on chestnut production, visit www.chestnuts.msu.edu, sign up to receive our newsletter and join us for the free 2023 MSU Chestnut Growers Chat Series. 

If you are unsure of what is causing symptoms in the field, you can submit a sample to MSU Plant & Pest Diagnostics. Visit the webpage for specific information about how to collect, package, ship and image plant samples for diagnosis. If you have any doubt about what or how to collect a good sample, please contact the lab at 517-432-0988 or pestid@msu.edu.

Become a licensed pesticide applicator

All growers utilizing pesticide can benefit from getting their license, even if not legally required. Understanding pesticides and the associated regulations can help growers protect themselves, others, and the environment. Michigan pesticide applicator licenses are administered by the Michigan Department of Agriculture and Rural Development. You can read all about the process by visiting the Pesticide FAQ webpage. Michigan State University offers a number of resources to assist people pursuing their license, including an online study/continuing educational course and study manuals.

This work is supported by the Crop Protection and Pest Management Program [grant no 2021-70006-35450] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.