|Schreiner, R Paul|
|SKINKIS, PATRICIA - Oregon State University|
|DREVES, AMY - Oregon State University|
Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2013
Publication Date: 2/1/2014
Citation: Schreiner, R.P., Skinkis, P.A., Dreves, A.J. 2014. A rapid method to assess grape rust mites on leaves and observations from case studies in western Oregon vineyards. HortTechnology. 24(1):38-47.
Interpretive Summary: A rapid method to monitor for the presence of grape rust mites on leaves or young shoots of grapevines was developed and tested. The rinse in bag (RIB) method was shown to effectively extract rust mites from single leaves placed in resealable plastic bags, allowing for easy counting under a stereo-microscope. The RIB method was less efficient in extracting rust mites from young shoots or dormant buds of grapevines. Early leaf stippling symptoms on grapevine leaves were also described and linked to the number of rust mites present. Surveys of rust mites on grapevine leaves using the RIB method provided evidence that in-season sulfur applications were effective in reducing rust mite populations in grapevine canopies. Supplies needed to the use the RIB method to monitor for rust mites are readily available, except for a moderate quality stereo-microscope.
Technical Abstract: A rapid method for extracting eriophyoid mites was adapted from previous studies to provide growers and IPM consultants with a practical, efficient, and reliable tool to monitor for rust mites in vineyards. The rinse in bag (RIB) method allows quick extraction of mites from collected plant parts (shoots and leaves) using either ethanol or isopropanol (35 to 70%) placed in a sealable plastic bag. The RIB method recovered ~ 85% of rust mites from leaves in the first rinse. The method is useful to estimate rust mites on young shoots (=10 cm length), although recovery of rust mites (average ranging from 35 to 81%) was lower due to a higher density of trichomes on young shoots as compared to leaf samples. The RIB method was not effective to assess rust mites within dormant buds, so a separate method employing a blender to disrupt tissues and extract mites in alcohol was developed. The RIB method was used to correlate rust mite abundance with leaf symptoms in commercial vineyards and nursery stock vines. The earliest visible symptom of rust mite damage on leaves in the summer was the development of stippling that is distinct from the type of damage caused by other grapevine pests. The stippling is described as numerous clear zones of small diameter (resembling pinholes) that are visible when a leaf is backlit. The degree of the symptom was correlated to the number of rust mites present on leaves. Scouting for early season stippling symptoms can be an effective way to identify potential rust mite problems early enough to allow for in-season management. Observations in commercial vineyards using the RIB method over two seasons showed that rust mite populations remain high on leaves until post-harvest. Canopy applications of sulfur effectively reduced rust mite populations when applied multiple times in early summer and also during mid-summer in a severely infested site.