Post harvest control in cherry
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Cherry leaf spot
Cherry leaf spot symptoms are variable around the state with some areas showing very few lesions while other regions have sustained significant defoliation as a result of the disease. Due to this variability, post harvest sprays will most likely be applied on an orchard-by-orchard basis. However, we have written some guidelines to help growers decide if a post harvest spray is warranted:
- If an orchard has been clean for the majority of the season with very few lesions and no defoliation, there is likely little need for a post harvest spray in this situation. This recommendation can be strengthened if a grower applied a fungicide application with his/her ethrel spray and because this block has made it through the majority of the season with little infection. A wet August, which is rare, will obviously increase the disease potential; a clean orchard now is less likely to have significant cherry leaf spot infection even under wet conditions. However, as we have completed harvest much earlier this year than in years past, we have a longer post harvest interval. Growers should monitor the weather and alter the no post harvest spray decision as the weather dictates.
- If an orchard had leaf spot symptoms during the season, even if the leaves look clean now, a post harvest spray should be applied. Lesions often lie dormant until fungicides are removed, and then have the potential to increase with low amounts of moisture in August – even a low amount of leaf spot in August will increase with fungicides removed from the system.
- If an orchard has had any kind of defoliation, then a post harvest fungicide spray is mandatory.
Bravo is the best post harvest option, but a reminder that this product is a protectant and must be applied before a rain event. There is no back action activity with Bravo.
Mites are another pest of concern post harvest, and in cherry twospotted spider mites can become particularly problematic under droughty summer conditions. As the groundcover vegetation becomes a poor food source for twospotted spider mites, they move up into the cherry trees in mid- to late summer. Older, inner spur leaves are often first infested as the females move to those locations first. However, with warm dry weather, mite populations can increase dramatically in a short time, and the mites will move off these older leaves to all parts of the tree canopy.
Scouting for mites can begin earlier, but now is a good time to be monitoring orchards for twospotted spider mites. One method of monitoring twospotted spider mites motile populations consists of sampling 25 leaves at each of 3 to 5 sites within a block, using 50% spur leaves and 50% shoot leaves.
- Two to three mites per leaf from mid-May to mid-June
- Five to seven mites per leaf from mid-June through July
- Ten to 15 mites per leaf in August
Presence of predaceous mites (greater than 1 per leaf) may justify delaying a treatment and repeating the cycle the following week.
Twospotted spider mite infestations may be controlled with a post-harvest miticide. When using chemical control, good coverage of all tree surfaces is critical. Some miticides are active on eggs (ovicides) and should be applied before egg-hatch; Apollo and Savey are miticides with ovicidal properties. Savey also works on mite larvae. An early application of superior oil does not work for twospotted spider mites as it does with ERM populations because first generation twospotted spider mites eggs are laid in the ground vegetation rather than in the tree. Other miticides are only active on motiles (adulticides) and should be applied after populations start to build: Nexter, Omite-CR (post-harvest only), and Vendex. Field evidence suggests Nexter is not as effective on twospotted spider mites as it is on ERM. Envidor is newly registered for mite control in cherries and is active by contact to all life stages. The active ingredient, spirodiclofen, controls mites by inhibiting lipid synthesis and is active by contact to all life stages. Envidor has a novel mode of action and is not known to have risk of cross-resistance with other currently registered miticides. Envidor 2SC has a rate range of 16 to 18 fluid oz per acre, 7-day pre-harvest interval for pome and stone fruits (14 days in grapes) and is restricted to one application per acre per season for all labeled fruit crops. With so many control materials from which to choose, and because of concerns with the development of mite resistance to miticides, no miticide should be applied more than once per year.