Wednesday, March 29, 2017

Apple scab and rust infection March 27-28

We recorded a 23-hr scab and cedar-apple rust infection period at our AREC March 27-28. Examination of rust galls indicated that cedar-apple rust basidiospores had discharged and some rust infection was likely. Apple bud stage ranged from 1/4-inch green tip to nearly open cluster on the most advanced varieties. Exposed blossoms are now also susceptible to quince rust. Hopefully, moderate wind conditions Thursday, March 30 will facilitate catching up with priority fungicide applications! 

Apple powdery mildew conidia were produced earlier this week, and March 30 will be a likely mildew infection day. 

Monday, March 27, 2017

Early season apple disease outlook, March 27.

Overnight wetting March 26-27 at our AREC, Winchester, ranged from 11 to 15 hr at 46-55 degrees and resulted in a possible apple scab infection period at the longer wetting interval. There was a rather wide range in bud stages during this wetting event, from tight cluster in the more advanced Granny Smith and Red Delicious to only 1/4-inch green tip in Golden Delicious, York, and Rome Beauty. 
Tight cluster stage on Granny Smith apple, Winchester, VA, March 27, 2017.

Mildew conidiospores were observed on Idared apple at early tight cluster stage (below) and conditions Monday afternoon, March 27 were favorable for infection. 

Mildew-infected Idared bud (center), compared to healthy fruit buds, upper left.

This extended wetting also brought maturity to the cedar apple rust teliospores on overwintering galls (below), as well as to quince rust spores in cankers on the eastern red cedar. It is not too likely that spores were available in time for rust infection to occur in the Winchester area during this wetting event, but consider additional wetting events this week as probable rust infection periods wherever rusts are an annual problem.

Cedar apple rust gall with mature telial horns.
A check of weather stations east of the Blue Ridge Mountains in Rappahannock County and central Virginia indicates similar length of wetting, and some at warmer temperatures. Generally, expect similar or more advanced stages of bud development and mature disease inoculum in these areas to the south and east. 

Sunday, March 19, 2017

Apple scab outlook!

Red Delicious bud stage March 18, 2017
Apple scab outlook: At our AREC in Winchester we had some early green tip on Red Delicious and other apples in early March, but they were still only about 1/4-inch green by March 18 (shown above). Apple scab ascospore maturation was initially delayed this year because of lack of snow cover and not much rain-wetting of leaves on the ground until March 6. We caught the first discharge of apple scab ascospores with five hours of wetting March 10. Snow cover March 13-17 helped to get the ascospore maturity up to date and more spores were discharged with melting snow and rain Friday night and Saturday, March 18. Expect abundant ascospore discharge with any additional wetting from here on out.  

Scab infection could have been possible in other areas such as Rappahannock County and central Virginia as early March 6-8 if buds and spore maturity were more advanced and where wetting may have been more continuous through that period. At Winchester we had several periods that could be lumped together as a split-wetting infection period.

It looks like bud development will continue to be slow over the next 10 days. We often suggest a copper or other protective fungicide spray before the first scab infection period of the season. Copper should not be applied to fresh market fruit after 1/4-inch green tip stage because of potential for fruit russetting. It looks like there will still be opportunity to apply copper in the Winchester area this week. Where there is concern that scab infection may have occurred in the past day or two, it would be prudent to add Vangard (cyprodinil) to improve post-infection control. Dodine (Syllit) is another early season option where scab may be the only apple disease of concern up to pink stage.

We applied our bud swell spray for peach leaf curl February 24 and the wetting March 6-8 was probably enough to cause leaf curl infection.

Remarkably, peach and apple buds at our AREC do not show much commercial freeze damage considering the many freezing nights that we have had with wind since the earliest green tip on apples and bud swell-pink on peaches.

As a reminder, we have installed a publicly accessible weather station at our AREC in Winchester. The station, which updates hourly, is located near the laboratory building at an elevation of 933 feet. This station is part of the NEWA system, so to access it one can either click on the  NEWA weather station locator map, or go directly to this URL: 
Explore the web site to view the numerous predictive programs that are offered there. We will refer to these more as the season progresses.