By Dr. Henry Wu
Mites are a part of life in the vineyard that warrants constant vigilance. As you know, they are not actually insects, but belong to the related class Arachnida, which also includes spiders, scorpions, and ticks. Two of the most common spider mites are the Pacific mite and the Willamette mite.
While small numbers generally don’t cause serious economic damage, exploding mite populations can cause major destruction and reduce yields and quality, meaning you must stay on your toes to stay ahead of them.
For this reason, monitoring is key to keep mites in check and to help PCAs and growers plan the best management strategies. Use the following hints to help in these monitoring efforts.
- Spider mites are quite small; adult females are about 0.5 millimeters long. The color of Pacific mite adult females ranges from amber to reddish, with relatively large dark food spots along the sides of the body.
- Willamette mite adult females are cream colored to pale yellow with small, dark food spots along the sides of the body. The male of each species has a pointed abdomen. Males are about half the size of females.
- Spider mite eggs are about 0.1 millimeters long, spherical, and transparent.
- Pacific mite eggs can be distinguished from Willamette mite eggs by the fine hair-like papilla that projects from the Willamette mite egg; Pacific mite eggs have no such papilla. Pacific mites produce webbing, whereas Willamette mites usually do not.
Divide and Conquer
To determine mite pressure, divide the vineyard into quadrants. In each quadrant, randomly select five vines each at least a few vines in from the end of the row. Look for mites on each of the 20 vines. Early in the season, choose one leaf between the second and fourth nodes on each of the 20 vines. Later in the season, choose the fourth expanded leaf from the growing tip. For more information on scouting, check out this mite monitoring resource from the University of California for thresholds and sampling instructions.
Keep in mind that damage can also help in identifying each species.
For example, Pacific spider mite damage begins as yellow spots. As damage progresses, dead (necrotic) areas appear on the leaves. High populations can make leaves nonfunctional due to leaf burning and bronzing, and large amounts of webbing. Damage is worse along the shoulder and tops of the vine canopies.
Willamette spider mite feeding in mid or late season causes foliage to turn yellowish bronze, but usually no burn occurs unless vines are weak. In red varieties, infested leaves may turn reddish.
The key to controlling undesirable mites while maintaining beneficial insect populations is to use the right chemistry at the right time.
There are plenty of options to help you do this, and one of the best solutions is Acramite® 50WS. It eliminates the majority of undesirable mites, giving beneficial insects a head start in keeping mite populations in control.
Acramite’s unique carbazate chemistry also makes it an excellent rotational miticide for resistance management.