April 25, 2000

WEATHER

Even with last week's rain, NW Michigan has received rainfall amounts well below normal. Young trees are always particularly susceptible to moisture stress if a drought were to materialize. If new orchards will not be receiving irrigation, then it may be a year to try particularly hard to get mulch around newly planted trees. The earlier mulch is applied, the better, as it will help reduce evaporative water loss from the soil.

GROWING DEGREE DAY ACCUMULATIONS as of April 24^th at the NWMHRS

Year        2000     1999    1998    1997
GDD42     214       189       245       103
GDD50       76         65       107          34

GROWTH STAGES:
Apricot: Harcot – first bloom
Plum: Stanley – green cluster
Apple: Red Delicious - early tight cluster
Sweet Cherry: Napoleon – early white bud
Tart Cherry: Montmorency – early bud burst
Grapes: Chardonnay - early bud swell

COMMODITY REPORTS

Climbing cutworms are just starting to be active in most tree fruits. Growers should keep a close watch on newly planted fruit trees for bud damage. Spotted tentiform leafminer first flight has started in apples. The first apple scab infection period of the season occurred last Thursday and Friday. This was a light infection in a few areas, and not all areas experienced an infection.

Green fruitworm trap catches are dropping off in tart and sweet cherry. Growers who are interested in using pheromone disruption for lesser and greater peach tree borer control should put the ties out the time of tart cherry petal fall. There should be no problem with putting them out now if it is easier. Ties should be hung at a convenient height -- shoulder high is fine. To avoid girdling, it is best to wrap ties around the branch, rather than twisting the ends up tight.

The first pear psylla hatch has occurred in pears.

Some strawberries without straw cover have experienced damage to the crowns, but much of this injury is healing. Growers with some injury should keep plants as stress free as possible.

GETTING THE MOST FROM ROUNDUP
by Gary Thornton, District Fruit IPM Agent

Roundup (Glyphosate) is a systemic herbicide that is widely used in fruit production in Michigan. In order for Glyphosate to be effective, it needs to be absorbed into the plant. In soft water Glyphosate has no problems in being absorbed; however; in hard water Glyphosate will be "tied up" and not be absorbed as readily. This is known as "hard water antagonism". Hard water contains high concentrations of the soluble salts, calcium (Ca++) and magnesium (Mg++). When these are present in your spray water, the Glyphosate, which is negatively charged, will combine with them to form Glyphosate-Magnesium and Glyphosate-Calcium compounds. The plant does not as easily absorb these compounds and the result is poor uptake and poor weed control. 

So how can growers increase the efficacy of their Glyphosate treatments? A common practice has been to add a surfactant to the spray tank; this allows the Glyphosate spray solution to spread across the leaf surface better and the result is greater absorption into the leaf. Many Glyphosate products now have the surfactant in them already, such as "Roundup Ultra". Roundup Ultra does not solve the hard water antagonism problem though, as the surfactant alone does not address this problem.

The hard water problem is best solved by adding 17 pounds of ammonium sulfate to 100 gallons of spray water. This has to be done prior to the Glyphosate being added. The addition of this compound to the spray water does two things. First, the sulfate ions tie up the calcium and magnesium ions by forming conjugate salts and secondly, some of the Glyphosate ends up as a Glyphosate-Ammonium compound, which some species of weeds preferentially absorb into their leaf tissue over Glyphosate alone. Urea-Ammonium Nitrate (28% liquid nitrogen) will also improve the efficacy of Glyphosate, but not as well as the Ammonium sulfate.

Reduced gallons of spray solution per acre will also have the effect of increasing the efficacy of the Glyphosate. Fewer gallons of water result in fewer calcium and magnesium ions to tie up the Glyphosate.

So if you have had less than ideal performance from your Glyphosate product and you think your water is on the hard side, then consider addressing the problem using Ammonium Sulfate.

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

Last Revised:4-25-00