Fruit Crop Pest Report- June 24, 2019

2019 Fruit Pest Update

June 24, 2019

2019 – 2020 Midwest Fruit Pest Management Guide

Below is a degree day comparison of the last five years. We are still about a week behind average and will likely continue this trend throughout the rest of the season. Things have really dried out this past week, offering some reprieve to the disease pressure.

Date 6/24	2015	2016	2017	2018	2019	5 yr avg
Base 50	472	548	515	623	348	521

INSECT & DISEASE CONTROL

APPLE

Disease Pressure – Apple scab ascospores are fully matured and almost completely discharged. Spores were still being caught in spore rods in central Michigan this past week, so although models are showing that spore are fully discharged, there may still be a chance for infection with a rain event. However, we are very close to being through primary scab season. A few apple scab lesions have been detected in sprayed orchards this past week. Apple growers can begin to increase intervals between protectant fungicides once primary apple scab season is over. Length of intervals can be increased to 2-3 weeks if scab lesions are not present on leaves or fruit. Apple growers who have scab lesions present in their orchards should continue to apply protectant fungicides on a regular schedule. Post bloom, there is no longer the possibility for fire blight blossom blight, but shoot blight and trauma blight are still possible. Risk of infection could increase this week if there is rain and temperatures are in the upper 70s, especially if there is any hail or damaging winds.

Insect Pressure – We have still not caught any plum curculio or spotted wing drosophila in traps. According to Michigan State University, only 5 SWD have been caught in the whole of Michigan so far. Plum curculio stings have been found in trees along fence rows in Door County, so they are active even though we haven’t caught any. A few random codling moths have been caught, but no successive trap catches, so biofix has not been set. Once we set biofix, the first cover spray should go out at 250 DD past biofix, followed by a second spray 10-14 days later.

The window for using chemical thinners is quickly ending as thinners don’t have much effect after fruitlets are 20mm or larger.

Apple fruit size of 3 varieties at PARS:

Zestar 20-25 mm

Honeycrisp – 16-22 mm

Cortland 15-20 mm

CHERRY

Disease Pressure – – Dry weather has slowed down cherry leaf spot infections a bit, but there are secondary infections taking place in many orchards. Cover sprays should still go out on a 7-10 schedule depending on rain events. With the increase in temperatures expected, copper products and Syllit should be avoided to avoid phytotoxicity. Do not use Bravo fungicides since fruit is past shuck split.

Insect Pressure – Cherry fruit fly traps will be placed in orchards this week. As mentioned above, even though there haven’t been plum curculio caught, stings are present on fruit. A protectant insecticide is recommended, since egg-laying could result in larvae be present in fruit at harvest. Make sure to check the preharvest interval of any product you choose. Cherries are not susceptible to SWD damage until after straw color begins to develop. Continue to scout for European red mites, especially in blocks where there has been a lot of use of pyrethroids for SWD control in the past few years.

Michigan State University recently published an article, “Low spray programs for tart cherry.” Just make sure to check that any product you use is registered for Wisconsin.

GRAPE

Mark your calendar for July 18, 3-5pm, for the 2019 Vineyard Walk at the Peninsular Ag Research Station!

Disease Pressure – Black rot has been detected in multiple grape varieties at the station. Check for tan lesions with small black dots around the edges, especially on older leaves. When scouting for diseases, former UW graduate student, Dave Jones, made an excellent photo disease guide per variety that can be found here.

Insect Pressure – A few flea beetle larvae and grape plume moth larvae are showing up. Larval damage rarely reaches economic levels.