Notes for 1st Weekend in May

May 1, 2015

Apple Scab and Fungicide Coverage!
Current forecasts for much of our region predict rain Sunday through Tuesday and is likely to produce the most significant ascospore release of the season. Temperatures over much of this period will be warm enough to produce scab infections with as little as six hours of continuous leaf wetness. Continuous is defined as all leaf wetness periods separated by less than eight hours.

If your last protectant application is approaching seven days ago you should consider “topping” it off or re-applying prior to these rain events. The forecasts suggest unsettled weather for much of next week, so getting your orchard re-covered then may be difficult.

Monitor Rainfall Accumulation
The standard guidelines for fungicide wash-off are after an inch of rain, half of the protectant is washed off and after two or more inches of precipitation all fungicide protection has been removed. These guidelines don’t consider the intensity of the precipitation. Half an inch of hard rain over 30 minutes will likely remove significantly more fungicide than half-inch of rain falling over twelve hours.

If you tank-mixed a single-site fungicide, e.g., any of the strobilurin, DMIs, class VII, etc., with your last protectant, a re-application may still be important. While these fungicides penetrate the leaf cuticle and are less susceptible to wash-off, their translocation into new growth is limited. With the higher temperatures forecast over the weekend leaf expansion will expose new, highly susceptible tissue. With excellent prior coverage the previously applied protectant will re-distribute to these areas, but obviously there is a limit to this process as well.

Finally, many of you are planting or working new trees this weekend. Be aware of the Restricted-Entry Intervals (REIs) for the fungicides you apply. Most, but not all, of the single-site fungicides have 12 hr. REIs, however the various brands and formulations of either mancozeb or captan have minimum REIs of 24 hrs.

Fire Blight Potential!
A few of our most southern orchards are at full bloom on Zestar, with other cultivars expected to open over the weekend. These orchards need to remember their fire blight risk will rapidly increase with the forecasted warm temperatures. By the evening of Sunday, May 3rd, the application of a protectant, e.g., streptomycin, other antibiotic, copper, or bacterial competitor, may be needed. With the exception of streptomycin all of these materials need to be applied prior to rainfall once the bacterial populations are high.

Don’t just eat your greens – See them too!
On a lighter note I thought I wanted to mention the incredible, ephemeral, annual transformation of our landscape now underway. Over the next few days scores of deciduous tree and shrub species will push out their first blossoms or leaves. The result visually is a panoply of shades of green that is stunning and changes by the day. Yesterday I counted fifteen shades of green on a single hillside.

A week or two from now most of these species will appear indistinguishable from a distance – they’ll simply be the woodlots and hillsides of our summer landscape – so if you’re able, find a vantage point soon and take a minute to get your five greens a day, visually!

Threshold IPM Services
Pest Management Consulting For Tree Fruit Growers
John Aue – Entomologist
17336 Merry Hill Rd.
Richland Center, WI 53581
Phone: 608 604-0234