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2016 Spider Mites and Dry Hot Weather

Anna Wallis, Tree Fruit and Grape Specialist
Eastern New York Commercial Horticulture

August 11, 2016

Spider Mites and Dry and Hot weather
Greg Loeb, Cornell Entomology
August 9, 2016

August is often the time we see the emergence of spider mite problems in vineyards and this summer it is particularly important to scout for them because we often see more mite problems under dry conditions. There are several contributing factors but temperatures are usually above average when its dry and these higher temperatures lead to more rapid mite development and more generations and potentially higher populations. Also, beneficial mites often are not able to keep up with the population growth of spider mites with hot temperatures. Perhaps an even more important factor is that with drought conditions the vines will shut their stomates during part of the day to help conserve water and this has the result of increasing leaf temperatures due to lack of transpiration and evaporative cooling. Also, the vine stops adding new leaves earlier in the season in drought conditions and this has the effect of concentrating mites on less leaf material. 
There are good reasons to scout your vineyard for spider mites and/or spider mite damage. I reviewed mites in my spring update, but briefly, there are two species of spider mites that attack grapes in the Eastern US, two-spotted spider mite (TSSM) and European red mite (ERM), but ERM typically is the more common. It is important to know the difference between the two species since some miticides are more effective against one than the other. As the name indicates, ERM is reddish in color and lays red eggs. Adult female TSSM tend to have large black spots on the top of the abdomen but this is a pretty variable. TSSM eggs are clear to opaque. TSSM tends to stay on the bottom side of leaves and produces obvious webbing while ERM can be found on either side of the leaf and does not produce much webbing. Both species have the capacity to go through a number of generations during the season. Because of their small size, it is often difficult to know if you have mites. Foliar symptoms (bronzing of leaves) are one clue, although if you have wide spread, obvious symptoms then economic damage may already be occurring. The working threshold for spider mites (TSSM and ERM combined) in our area is 7 to 10 mites per leaf, although this will vary depending on health of the vineyard, crop load, value of the grape, etc. The impact of mite feeding on grapes includes reduced photosynthesis, delayed accumulation of sugars thereby delaying harvest date, and the potential of reduced yield the following season. I suggest sampling at least 50 mid-shoot leaves from both the edge and the interior (25 leaves each) of a vineyard block, examining both sides of the leaf. A hand lens will be necessary to see the mites for most people. Even with a hand lens, it is challenging to count the mites. Thus, we recommend estimating the proportion of leaves infested with one or more mites and use something like 50% infested as a treatment threshold. A leaf is considered infested if it has one or more spider mites. Remember to keep rough track of which species is most common.
There are several chemical options available for mite control in New York and Pennsylvania: Vendex [fenbutatin-oxide], Agri-Mek and several generics [abamectin], Nexter [pyridaben] (not on Long Island), Acramite [bifenazate], JMS Stylet Oil [aliphatic petroleum distillate], Zeal Miticide1 [etoxazole], Onager or Savey [hexythiazox], Danitol [fenpropathrin], Portal [fenproximate] and the newly labeled miticide called Nealta [cyflumetofen]. Read labels carefully. JMS Stylet Oil is not compatible with a number of other products including Captan, Vendex, and sulfur. Also, although Stylet Oil can help with mite problems, it is not likely to provide complete control in problem vineyards. Nexter is very effective against ERM but higher rates should be used for TSSM. Agri-Mek currently has TSSM on the label but not ERM, although in apples both species are on the label. Acramite includes both TSSM and ERM, although it calls for higher rates for ERM. The new label for Zeal miticide 1 includes both ERM and TSSM in NY whereas the old label only had TSSM. You need a 2(ee) recommendation, which is readily available, for use against ERM with older material. Since Zeal miticide 1 affects eggs and immatures, it is advised to apply before populations reach damaging levels to give the material time to work. Similar advice can be applied to Onager, Savey and Portal. Danitol and Brigade (two-spotted only) are broad-spectrum insecticides that also have fairly good miticidal activity. Pyrethroids are hard on beneficial mites, however.

Spider mites are often thought of as a secondary pest. In other words, something must happen in the vineyard that disrupts their natural control by predators, particularly predatory mites, before their populations can increase to damaging levels. Since Danitol and Brigade have miticidal activity they would not be expected to flare spider mites in the short term. However, in the past, spider mites have been quick to develop resistance to frequent use of pyrethoids. This may or may not happen but it is worth keeping in mind. One of the first things to watch out for is initial good suppression of mites followed by a resurgence indicating the spider mites recovered more quickly than the predatory mites. The other miticides (Vendex, Onager, Savey, Zeal, Acramite, Nealta, and Nexter) are generally pretty easy on natural enemies, although at high rates Nexter can negatively affect predatory mites. Overall, paying attention to conserving predatory mites can pay economic dividends since miticides are quite expensive.

In summary, given how dry things are its worth getting out in the vineyard and scouting for mites and mite damage. While you are out there, also scout for grape berry moth and leafhoppers. As of today (August 9, 2016) we are at about 1600 DD using the grape berry moth phenology model (in Geneva, NY) at the NEWA web site (http://newa.cornell.edu/), so its about the right timing for the third flight of grape berry moth. As we get closer to harvest, you also will want to be cognizant of multicolored Asian beetle in clusters and Drosophila fruit flies (see my spring review for more information). 
For questions, contact Greg Loeb, Cornell Entomology at gme1@cornell.edu 315-787-2345.






European Red Mite (jpg; 15KB)
  • Adult European red mite on bottom side of leaf


Two Spotted Spider Mite (jpg; 11KB)
  • Two spotted spider mite adult. Photo: Jack Clark, UC Davis


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Upcoming Events

Ag Manager Webinar Series: Ag Tax Topics - Sales Tax and Property Tax Issues for Ag in NYS

August 27, 2019
12:30 - 12:50pm

Join Liz Higgins from the CCE ENYCHP every other Tuesday at 12:30pm throughout the summer as she discusses pertinent business topics for busy farm managers.
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Willsboro Farm High Tunnel Twilight Meeting

August 27, 2019
5:00pm - 7:00pm
Willsboro, NY

Join vegetable specialists Elisabeth Hodgdon, Jud Reid, and farm manager Mike Davis for a high tunnel and field tour at Cornell's Willsboro Research Farm, where they will share research results for the following projects: 
  • Striped cucumber beetle management suing netting and row cover
  • Varietal differences in cucumber susceptibility to striped cucumber beetle
  • Ground cherry and goldenberry production in field and high tunnel environments
  • Overwintered high tunnel spinach nitrogen fertility 

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Announcements

Resources from CCE ENYCHP!

We are developing new ways to connect with the CCE ENYCHP team this year! We have a Youtube page located at this link. Check out videos on Table Grape Production, Pest Updates and the 20 Minute Ag Manager - in 4 Minutes series

We have a Facebook Page here as well as an Instagram page. We keep these places updated with current projects, events, and other interesting articles and deadlines.

There are also text alerts available. Fruit and vegetable farmers in 17 Eastern NY counties can now receive real time alerts on high risk disease and pest outbreaks texted directly to their cell phone. The Eastern NY Commercial Horticulture program, which is supported by local Cornell Cooperative Extension associations, will now offer text alerts to those that enroll in our program in 2019. 

The text alerts will be reserved for important crop alerts that could impact management decisions immediately. For instance, if there were an outbreak of Late Blight in the area, this would be transmitted to vegetable growers.

Farmers can choose the crop for which they wish to receive updates. Additionally they can request that Ag Business Alerts be sent to them. These alerts might include due dates for crop insurance deadlines, market opportunities etc.

If you have questions, please contact enychp@cornell.edu


Podcasts

Biweekly Vegetable News Podcast - Episode 9 - 08/21/19

August 21, 2019
The August 21st, 2019 edition of the Eastern New York Vegetable News covers the following topics:

Changes to Worker Housing Regulations in the Farmworker Fair Labor Practices Act (1:25)
Managing Alternaria Leaf Spot and Head Rot on Broccoli (4:25)
Gauging Winter Squash Maturity for Harvest (10:05)
Insects in Hemp, especially European Corn Borers (18:33)
Guidance on the Dropped Covered Produce Provision of the Food Safety Modernization Act (22:53)
Cucurbit Downy Mildew Management Update (27:02)
Report from the BioControl Field Day and Weed Management Recommendations (31:07)
Day Neutral Strawberries (40:33)

Here are links to additional resources mentioned in the episode:

Current Housing Regulations for Seasonal and Migrant Farmworkers
(On January 1, 2020, these will now apply to farms housing any number of seasonal and migrant farmworkers)

Public Health Law, section 225, NYCRR Title 10 Health, Part 15, Migrant Housing: https://www.health.ny.gov/regulations/nycrr/title_10/part_15/

Managing Alternaria Leaf Spot and Head Rot in Broccoli

Sue Scheufele “Can Alternaria Leaf Spot Be Managed Organically?” http://www.hort.cornell.edu/expo/proceedings/2013/Cole%20Crops/Cole%20Crops%20Scheufele%20Alternaria.pdf

Christy Hoepting “Control of Alternaria head rot in broccoli featuring exciting results from 2018 on‐farm fungicide trial” http://www.hort.cornell.edu/expo/pdf/20190115-all-day-hoepting.pdf

Dropped Covered Produce:
FDA Factsheet on Dropped Covered Produce: https://www.fda.gov/media/129568/download

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