Reminder- meeting tonight

This is a reminder that tonight is our first In-Depth Meeting of the year, 7:00 – 8:30 p.m at our AREC. Following Chris Bergh’s entomology update, I will discuss Early Season Apple Disease Management and Positioning of Newer Fungicides. Pathology updates will be included in the discussion.

Please note these additional dates for meetings at our AREC:

Thursday, April 14: Breakfast Meeting 7:00 – 8:00 a.m. Pathology, Entomology and Horticulture updates and breakfast provided.
Following this meeting, at 8:30 AM, a memorial tree and stone plaque will be dedicated in memory of horticulturist, Dr. Rongcai Yuan, on the anniversary of his passing last year.

Thursday, April 28: In-Depth Meeting 7:00 – 8:30 p.m. Pathology, Entomology and Horticulture updates. Fruit Thinning discussion with Drs. Greg Peck and Steve Miller.

Thursday, May 12: Breakfast Meeting 7:00 – 8:00 a.m. Pathology, Entomology and Horticulture updates and breakfast provided.

Thursday, June 2: In-Depth Meeting 7:00 – 8:30 p.m. Pathology, Entomology and Horticulture updates; and Speaker/topic to be announced.

Can we get scab infection with snow?

The really unusual weather we've had so far this spring, and a forecast for who knows what the next two days or so, brings up the old question about whether it is possible to have an apple scab infection period with wetting by melting snow. The answer, of course is, yes it is. If there is enough wetting to initiate ascospore discharge and deposition on susceptible tissue in the tree, then prolonged wetting from melting snow (48 hr at near freezing temperatures) can result in infection. We saw it happen in 1990- a year that gave us three snows and 13 nights below freezing after green tip - and we still ended up with decent apple and peach crops.  Logic says that if the snow blankets frozen ground before ascospore discharge, it would prevent discharge into the air, negating impaction of the ascospores in the tree and therefore would not result in infection.

Speaking of the wild weather this spring, without looking back, I don't recall a year when we had this much prolonged cold after green tip. So far, at the AREC, we see only a little damage of king bloom that was showing some color (a little bit beyond tight cluster) Sunday morning when the temperature dipped to 26. The coldest time seemed to come with the snow and there was probably air movement that brought cold to higher elevations in the orchard blocks that were more advanced than lower areas (a freeze rather than a frost). Once we get through this, hopefully the week or more of colder weather will be recognized as having been beneficial because it delayed bud and reduced susceptibility to later frosts.

Wetting March 23-24

At our AREC we recorded wetting from 7:15 PM Mar 23 - 10:30 AM Mar 24, about 85% of the duration of wetting required for scab infection at temperatures that ranged from 49F down to 37F. But temperatures and area showers were variable earlier on March 23 and some local areas may have had their first scab infection. Wetting occurred north of Winchester by 6 PM while the temperature was at 55F; other areas had showers near noon March 23 and may have remained wet longer. Scab protectants applied before this wetting probably weathered through the rainfall which totaled about half an inch. At our AREC, apple bud stage varies from 1/2"- green for York (shown above) and Rome to tight cluster for several cultivars including Gala, Red Delicious and Idared. Where no fungicides have been applied and length of wetting is marginal or in doubt, it would be prudent to include one with after-infection control in the first application. Also, consider that powdery mildew spores are now available for infection during dry weather 53F and higher, and cedar-apple rust gall spore horns are extended to more than a half-inch, indicating potential for rust infection with the next rain in the mid-50s and higher.

Apple powdery mildew

Today Idared apples were at tight cluster with some petal color showing through as seen in the first picture below. The second picture shows a healthy bud on the left and a reddish, mildewed bud on the right. Although much of the exposed surfaces appeared to have been "washed off" by recent rains, as suspected there were abundant mildew spores (conidia) present on the more protected surfaces (last picture). Cool, damp weather is more conducive to scab development than mildew but it is obvious that spores will plentiful when the temperature turns warmer again (53F+).

Apple bud stage March 21

This morning nearly all apple cultivars at our AREC were showing some green. Above is the same Red Delicious bud that I pictured last Thursday. (The dark brown vertical structure is a leaf petiole hanging on from last year). Red Delicious fruit buds are at or near 1/2-inch green. Idared is a little more advanced with some cluster leaves curling back as they do for tight cluster stage.

The thunderstorm this morning gave us 0.45 inch of rain but it wasn't wet long enough for scab infection. Showers are forecasted again for this evening and tomorrow evening.

Outlook for next week

This year is starting out reminiscent of last year when we caught some apple scab spores and then had an infection period several days later.  A protectant spray of copper, mancozeb, or ziram before that first infection period and later protectants would have greatly diminished the threat of scab through much of April, but a delayed application after the first infection period required something with some after-infection control to prevent the appearance of lesions and re-infection two weeks later.

A chance of showers from tomorrow evening (Sunday, Mar 20) through Monday evening at temperatures in the mid-40s and warmer could again lead to early infection, assuming that most blocks in the Frederick County are not yet covered with a fungicide. In case there is an infection period, remember that follow-up sprays of copper or an EBDC fungicide alone do not have after-infection control. We have found that Vangard can be tank-mixed with copper or mancozeb to improve after-infection control in these early season situations.

We have applied oil to most of our fungicide test blocks in anticipation of increased mite populations later in the season if we need to step up controls for Brown Marmorated Stink Bug (BMSB). Remember to leave 7-14 days between an oil spray and sprays of captan or sulfur. We did not apply oil to the Red Delicious fungicide blocks to see if increased mite populations will aggravate the Alternaria Leaf Blotch that causes defoliation of Red Delicious, that has been observed for several years and might reappear this year.

It's a new season!

Apple scab ascospores were trapped during rains March 15-16. Red Delicious and Idared cultivars were showing some early greentip at our AREC the morning of March 16 but the 18-hr wetting was not long enough for infection at mean temperature 40° F.



Red Delicious fruit bud 3-17-11