Drift Monitoring


by WSU

by OSU

A publication on how to reduce drift when spraying.

Penalty Schedule 

WAC 16-228-1220 Damage to land, humans, plants

Endanger, environment, food

RCW 17.21.150  Faulty, careless, negligent


From the Washington State Department of Agriculture-Pesticide Management Division:

No one expects their crop to be exposed to herbicide injury but it occurs somewhere every growing season. Damage from herbicide drift can cost a grower hundreds of thousands of dollars in crop loss, reduction of wine or juice quality, and serious harm to grape vines that can reduce future production. Traditionally, it has been phenoxy herbicides, such as 2,4-D, that have been responsible for the bulk of herbicide damage observed on grapes, but now more damaging chemistries are available for use in this region. Among them is a chemistry that interferes with nitrogen metabolism, thus rendering useless the application of water and additional nitrogen to herbicide affected vines.


The Department of Agriculture asks for your cooperation to better assist with an investigation. It is essential that the complexities of herbicide damage to grapes are understood as well as the need to adequately prepare appropriate information regarding grapes prior to filing a complaint with WSDA.


It is very important to fully understand both the quantity and quality of information required before a thorough and effective investigation can proceed. Research by WSU-FEQL and the Department of Agriculture-Pesticide Management Division has provided grape producers with tools to provide critical and necessary data for an investigation’s proper procedure. Your observations are management tools for critical decisions regarding irrigation, nutrition, and reliably reporting information to us.


When an exposure to an herbicide occurs there is a critical lag time between the exposure event and the subsequent expression of symptoms. During this same time period perhaps hundreds of pesticide applications may have occurred that are similar or identical to the one affecting the grapes in question. Most critical herbicide exposures occur over a 12 week period beginning with bud break, but some may occur later in the growing season. It also must be considered that modern pesticides are rapidly metabolized by the affected plants and degraded in surrounding areas, thus making reliable laboratory analysis difficult or impossible to achieve. With this in mind, it is essential that WSDA personnel only accept crop history data, from bud break onward through each leaf emergence (leaf indexing), which has been collected by on-site vineyard personnel.


Washington’s grape growing regions are not protected by isolation.  Grapes are sensitive to many pesticides used to produce other crops both locally and throughout the ag region, including other states. WSDA strives to protect grape production through the restriction of phenoxy herbicides for use by only certified applicators and through various county rules that apply to nozzle/pressure use, daily start and stop times to avoid air temperature inversions, and more. Also bear in mind that many out-of-state based pesticide applicators working in Washington are unaware or avoidant of local conditions and/or state requirements, and pesticide applications which occur on Federal lands do not fall under WSDA purview.


We hope that growers realize and appreciate the enormity of evidentiary requirements faced by an investigator in any complaint scenario and the utmost importance of accurate and detailed information gathered by grape growers prior to filing a complaint. Failure to provide this required information to an investigator renders it impossible to proceed with a fair and accurate investigation. WSDA investigators approach each investigation with the knowledge that its findings may be pertinent to litigation. The most WSDA can do for a grape grower not performing the required leaf indexing is simply document the allegation(s) of a complaint without investigating any of its elements. Remember, “It is a violation of WSDA rule to provide false or fraudulent information.”


We hope you can take the time to familiarize yourself with the training and reporting information provided at the WSU-FEQL website: http://feql.wsu.edu/eb/index.html. If you require further assistance contact a WSDA-PMD representative at:  Toll-free 1-877-301-4555  See the website at: http://agr.wa.gov/PestFert/


Thank you.




For leaf indexing technical assistance contact

Gail Amos, WSDA 509-249-6930 or email gamos@agr.wa.gov

Vince Hebert, WSU-FEQL 509-372-7393 or email vhebert@tricity.wsu.edu

Bruce Olson, WSDA 509-665-3395 or email bolson@agr.wa.gov




The off-target movement of cereal grain broadleaf herbicides to grape vineyards has affected grape production in the Pacific Northwest over the past 30 years. Although sound management practices have been implemented to reduce chemical drift, vineyard injury still remains a concern. Continued grower involvement in monitoring plant symptomology from phenoxy-type herbicide exposure (i.e., exposure from airborne 2,4-D, dicamba, MCPA) will be key to identifying the impact of herbicide drift on grape production.


Leaf indexing must accompany any herbicide-exposure complaint to the Washington State Department of Agriculture (WSDA). Leaf indexing is a simple process and can provide valuable information on symptoms of herbicide injury. This Website provides a leaf-index guideline for dating exposure, which is critical to an herbicide injury investigation. Leaf-position dating is important because of the lag time between the exposure and the appearance of symptoms. Leaf indexing must be performed weekly by the vineyard operator/assistant from bud-break through full bloom or through vine hardening.


Leaf Index; and Report of Loss forms are available as links from this page. An example of a completed Leaf Index form is also provided.


Leaf Index


To begin leaf indexing, select some representative shoots for observation. The vines from which shoots are chosen should be mature and typical of the vineyard. The number of shoots selected will depend on your time and ability to observe the shoots on a weekly basis throughout the growing season; a minimum of three is recommended. The variety selected for observation will not be as important as selecting a set of varietal shoots that you will be able to observe weekly throughout the season. The selected shoots are not to be pruned during the observation period.


Note: While phenoxy-type symptoms generally look similar regardless of the variety of grapes, there are certain varieties that can exhibit herbicide-exposure symptoms more readily than others. In most cases, the white varieties will exhibit greater herbicide symptomology than other varieties.


Mark the selected shoots with flagging tape or other physical marker that will be easy to see. This will aid in finding the correct shoot again. Alert the field crew that flagged shoots should not to be pruned. The flagged shoot must be kept upright during the observation period.



Figure 1


Do not flag the actual shoot you will be observing. Attach flagging material to main stem near shoot. It is also a good idea to flag the end of the row so you can quickly find the flagged vine.


Make Vine Observations


Weekly observations and accurate documentation of when leaves unfurl provide the most important information for an herbicide-injury investigation. Regularly record on the Leaf Index form or in your observational notebook the date and the number of leaves expanded on your selected shoots. Include leaf appearance and any other observations that may be important for documentation as well as for your own learning experience. The WSDA Leaf Index should accompany your notebook entries.



Figure 2


A leaf is considered expanded when the leaf unfurls.


Designate the first leaf that opens (basal) with a "1," the next leaf with a "2," and so on. Record this information in your notebook. Leaves may be marked with a "bullet-point" Sharpie marker after the cutin has formed for easy reference on follow-up observations.



Figure 3


Write the leaf number directly on the leaf.


Select shoots and make observations on a weekly basis from April-July


Use flagging tape to mark indexed shoots


Label leaves with permanent marker after cutin formation


Record date and weekly observations in a notebook/logbook and/or WSDA report forms (Leaf Index) (Report of Loss)


Keep observation shoots in upright position




Document Vine Development with Photos


Photographing your flagged vines is not required but can be useful to ensure complete documentation. A digital camera is ideal for this because you can immediately determine if the photo is clear and accurate, and you can readily download the photo to a computer for archiving. Additionally, a photo can be electronically sent to WSDA for evaluation when questions arise.


Get a clear photo of each mature leaf. You may take useful photos up to a week after the date the leaf expands. When photographing the leaves, use a backdrop such as a board with a dark piece of cloth covering it so the leaf will be more visible in the photo. Also, ensure the date is somewhere in the photo. This can be easily accomplished by printing the date on a colored address label or colored label tape on the backdrop. White labels can cause a glare in the photo making the date unreadable.



Figure 4


Be sure the date the photo is taken appears somewhere in the photo.


We suggest downloading and labeling the pictures as soon as possible after the observation and placing the pictures in chronological order. Below each leaf picture, include the leaf number and any observations you have made. By doing this, you have a visual history of each leaf on a selected shoot. This documented visual reference will aid in a proper investigation.


Assess Phenoxy-type Herbicide Symptoms


Exposure to a phenoxy-type herbicide before cutin formation will cause a leaf to show herbicide-exposure symptoms. The leaf will not grow out of these symptoms. These symptoms can range from mild to severe as illustrated below.



Figure 5


Normal leaf



Figure 6


Abnormal leaf margins

The leaf margin is the outer edge of the leaf.



Figure 7


Reduced or lack of sinus

Sinuses are the large indentations of the margin normal in a grape leaf.



Figure 8


Vein clearing

The color is gone from the veins in the leaf.



Figure 9


Parallel veination

The veins are nearly parallel to each other from base to tip of leaf


Rate Leaf Symptoms


Individual leaves can be rated using the Severity Rating. The rating ranges from 0 to 5 with 0="no observable phenoxy-type symptoms" and 5="severe phenoxy-type symptoms." Use the photos and documented field descriptions to aid in rating symptoms.


Severity Rating  



No visible symptoms of phenoxy-like herbicide exposure. Margins and lobes are well defined. No apparent rugose texture.



Possible rugose (bumpy) features on leaf surface. Slight shortening of lobes and sinus. The leaf will grow to normal or near normal size.



Rugose features as well as disfigured margins. The leaf will be noticeably, but not significantly, smaller than leaves with a lesser rating.



Deformation of leaf margins. Has diminished or possible lack of sinus. Lobes may be blunt. Lighter leaf color. Leaf will be significantly smaller than those with a lesser rating.



A definite deformation of leaf margins and sinus. Noticeable vein clearing. The leaf will be very stunted in size.



The leaf will be severely dwarfed. Veination will be parallel. The margins may resemble the end of a straw broom. Grossly deformed leaf.