Fruit Crop Pest Report- June 3, 2019

2019 Fruit Pest Update

June 3, 2019

2019 – 2020 Midwest Fruit Pest Management Guide

Apples are at king bloom to full bloom and cherries are at petal fall. On average, grapes have 2-3″ shoots and the first leaf is separating from shoot tips.

Weather the last week has been all over the board. At the Sturgeon Bay Enviroweather station, temperatures reached a high of 86ºF on May 31, and two days later, reached a low of 32ºF.

For apples and tart cherries at full bloom, critical temperatures for 10% flower bud kill are at 28ºF or 90% flower bud kill are at 25ºF. Click the link below for more information on tree fruit crop bud cold temperature injury.

Tree Fruit – Critical Temperatures

Below is a degree day comparison of the last five years. We are still about a week behind average.

Date 6/3	2015	2016	2017	2018	2019	5 yr avg
Base 50	254	279	196	351	145	261

INSECT & DISEASE CONTROL

APPLE

Disease Pressure – Apple scab infection periods continue to occur at all the stations. With temperatures in the mid-50s to 60s, there will be an infection period if leaves are wet for 9- 11 hours. Apple scab spray programs should be ongoing to protect apple scab susceptible varieties through the end of primary scab season; typically mid to end of June in Northeast WI (it likely will be a bit later this year).

Apples are susceptible to fire blight if blossoms are open and temperatures are over 60ºF. Any wetting (rain, fog or dew) can then trigger an infection. Protectant applications of a bactericide should be made every 4-5 days during the bloom period.

Insect Pressure – Do NOT use insecticides during bloom that harm pollinators. A light spotted tentiform leafminer is continuing, but no other insects were caught last week (coding moth, plum curculio, green fruitworm, or obliqubanded leafroller). Continue to scout for green fruitworm and obliquebanded leafroller damage through petal fall as there has been some light blossom feeding being observed.

Plum curculio emergence is determined by moisture and temperature. We have had enough rain this year, so temperature is likely the limiting factor. We could expect to see plum curculio emerge if 1) average temperatures between 55 and 60ºF for three to four days, 2) average temperatures above 60 F for three days, and 3) maximum temperatures of 75ºF for two consecutive days. Keep in mind that these are average temperatures, not highs, so we are likely behind normal emergence.

At full bloom, consider crop load and use flower and fruit thinners as needed. There has been substantial information about precision thinning tools in the Wisconsin Fruit News which can be found here: https://fruit.wisc.edu/crop-management-newsletters/

CHERRY

Disease Pressure – – Cherries are now susceptible to cherry leaf spot, so fungicide programs should be ongoing. The risk for European Brown Rot has decreased with warmer temperatures, but could be an issue if trees are in full bloom and we get more cool, wet weather.

Insect Pressure – So far there haven’t been any plum curculio adults or spotted wing drosophila flies caught in traps. Continue to scout for green fruitworm and obliquebanded leafroller damage through petal fall.

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 – Fungicide applications can begin around 4” – 6”growth

Insect Pressure – Buds that haven’t burst could still be susceptible to grape flea beetle damage. Numbers at the Peninsular Station were very low.