WEATHER

Strong winds hit NW Michigan with reports as high as 60 mph, causing some tree damage and the potential for fireblight spread. Evaporation rates have increased with the recent heat and wind. Evaporation at the NWMHRS this past week was 1.48", indicating about 1.11" of moisture is desired for tree fruit. Rainfall at the NWMHRS was 1.28".

GDD 50: 515; GDD 42: 941

GROWTH STAGES:

Apricot: Harcot – 25mm fruit
Plum: Stanley – 17mm
Apple: Red Delicious - 20mm
Sweet Cherry: Napoleon – 14mm
Tart Cherry: Montmorency – 13mm
Grapes: 24" shoots

COMMODITY REPORTS

Apples - Scab primary season is over.  Growers should have followed up the heavy infection period of 5/25 with a back up spray. This spray, if a protectant was included, should have concluded the primary season.  Fireblight strikes are now clearly visible where strep sprays were not applied, or where application was inadequate. Sunday's strong winds created a trauma blight for apples and pears. Codling moth trap catches remained steady. Growers who are not trapping should biofix on 5/19 and will need to spray immediately.  Growers who biofixed on June 1^st are currently at 115 DD base 50 and, with this heat, will probably need to spray by June 14^th. Plum curculio are active in commercial orchards.  Spotted tentiform leaf miner trap catches are down.  Green apple aphid colonies are developing. 

Cherries - It is not too late for Gibb sprays to be applied to tart cherries.  Applications should be made in the evening on bearing trees when temperatures are closer to 70 degrees F to avoid too much of a response when applied in daytime temperatures above 85 degrees.  Cherry leaf spot infections from the 5/19 rain are common on the lower parts of trees where alternate middle row sprays have been applied to control past heavy infection periods.  Full covers are needed to best control a heavy infection period.  Both sweet and tart cherries need to be protected against plum curculio until their egg laying ceases. Green fruitworms are pupating; larvae are 1 1/4" long.  Brown rot pressure has been high with the recent high humidity.  As sweet cherries start to turn color, growers should tighten up their schedules and switch to better fungicides.  European brown rot is showing up in the Northport area on Montmorency.  It causes a spur blight much like fireblight on apples.  European brown must be controlled at bloom. Powdery mildew is showing up on the underside of tart cherry leaves.  Growers should be putting on trunk sprays when the wind allows it. 

Plums should be checked for mites and a miticide applied if you find over 5 mites per leaf. Thiodan should be sprayed as a trunk spray to protect against borers. Plum curculio remains a threat. 

Peaches and apricots should be protected against tarnished plant bugs and other plant bugs, particularly if the orchard is mowed or a nearby hayfield is cut.  Trunk sprays can be applied. Plum curculio remains a threat. 

Grapes - Powdery mildew will be heavy this year.  The prebloom fungicide spray will be extremely important in controlling this disease this year.

Strawberries - Harvest will get underway by the end of the week.  Consider using irrigation during periods of high heat to help cool berries. We are not aware of any serious pest problems at this time.

MISCELLANEOUS

2,4-D Application Caution
By James E. Nugent, District Horticulturist, MSUE 
Gary E. Thornton, District Fruit IPM Agent

The preharvest interval for 2,4-D on stone fruit is 40 days.  It is too late for application on most sweets and many tart cherries. However, where it can be applied, avoid 2,4-D applications in heat.  Do not apply 2,4-D when temperatures are predicted to be in the mid 80-'s and above.  For orchard application we use the amine form which has much lower volatility than the ester form, but still the amine will volatilize under high heat.

Avoiding Problems with Water Soluble Packaging
By Jim Nugent and Gary Thornton

Water-soluble packaging has greatly enhanced the convenience and safety of handling wettable powder pesticides. However, dissolving the packages can be affected by a few factors. To avoid problems, consider the following:

• Boron in the spray mixture turns the packages to a jelly that quickly plugs screens. If using boron in the spray, always completely dissolve soluble packages prior to adding boron.

 

 

If boron was used in the prior tank, there will be some residue in the mixture left in the bottom of the tank. In the case of dilute to moderate concentrate mixtures, we generally do not see problems if not too much of the mixture is left in the bottom of the tank and if the tank is then at least 75% refilled with water prior to adding the soluble packaging. Problems are much more apt to occur when using high concentrate mixtures (this results in more boron remaining in the mixture in the bottom of the tank), when a larger amount of mixture is left in tank, or when packages get added after refilling the tank only a little way. If any of these potential problem situations occur, then either pre-dissolve the packages prior to adding to the tank or rinse out the sprayer prior to refilling.
 

• Other heavy metals are also reported by the manufacturers to cause problems for the packages. In practice we have only seen the problem with boron, but still keep in mind that other heavy metals may also have an effect.

• Packaging dissolves best in 6.0-6.5 pH water and more slowly in high pH water (it still dissolves, it just takes longer). If high pH water is being acidified, it may be desirable to acidify prior to adding water-soluble packaging.

• Packages also dissolve more slowly in cold water.

Apple Thinning
By Jim Nugent and Phil Schwallier
MSUE District Horticulturists

Now is the time in NW Michigan when we can assess the impact of the apple thinning applications made on May 27-29 (a time when a good deal of thinner was applied). In those cases where a second application is required, it will need to be applied this week when temperatures are predicted to be very high. So here are some factors to consider when thinning under very high temperatures.
 

• NAA gets more active with higher temperatures. For expected temperatures in the upper 80's to lower 90's, reduce rates about 25% when using NAA alone. If tank mixed with Sevin, suggest reducing NAA rate by 30-40%.

• Sevin is very temperature dependent (even more than NAA), i.e., it is not effective when temperatures are cold and it's very effective when temperatures are hot. Therefore, expect more thinning from Sevin under hot conditions would normally occur. Because the effect of Sevin is not as rate dependent as NAA, it should still be applied at or above the lowest recommended rates but avoid applying at the highest rates during a period of high temperatures. For Sevin XLR, the lowest rate would be 1 pt/acre for medium size trees and 1 1/4 to 1 1/2 pts/acre for large, standard trees. 

• In situations where moderate thinning with a low rate of NAA plus Sevin would normally be used, consider using either NAA or Sevin alone under conditions of high heat. If aggressive thinning is needed, then the tank mix of NAA and Sevin could still be used, but decrease the NAA rate 30-40% and use the 1 pint/acre rate of Sevin. 
 

Please send any comments or suggestions regarding this site to: 
Bill Klein, kleinw@pilot.msu.edu

Last Revised:6-8-99