Walnut Husk Fly, Irrigation, TRAPs Website
June 29, 2012
In this Issue:
What to Look for/Do Now:
Current Insect and Disease Activity
We have received reports from Layton and other areas of northern Utah that walnut husk fly has been found, so it is now time to treat black and English walnut trees for this pest for all areas of northern Utah. Late peach varieties are also susceptible, where they are growing near walnuts. Emergence will continue to late September, with peak emergence to occur starting the week of July 23.
This is a full month earlier than last year, which unfortunately means more treatments on the walnuts. Begin sprays now, continuing at regular intervals until the walnuts are within 1 month of harvest. Eggs laid later than this will not have time to develop and cause damage. If you are not sure if you have walnut husk fly, you can hang a Pherocon AM yellow sticky trap (purchase online or by phone from Great Lakes IPM). The flies are identified by their wing pattern.
If you don’t mind the extra work of removing the damaged husks, treatment on walnuts is not entirely necessary because the kernel is usually not damaged. Storing the infested nuts in a damp burlap bag for 2-3 days will help in husk removal.
Early walnut husk fly feeding on young walnuts causes the nut to shrivel, turn moldy, and drop prematurely. Later feeding (late Aug. – Sept.) will not affect the kernel, but will result in a husk that is stained black and a hull that is difficult to separate from the nut. The maggots feed for 3 to 5 weeks before dropping to the soil to pupate.
Options for backyard trees are spinosad (Green Light, Gardens Alive Bull’s Eye, Monterey) which is applied every 7 days, or acetamiprid (Ortho Flower, Fruit, and Vegetable), which is applied every 14 days. Make sure you cover the entire tree.
Another option is using a bait with spinosad. The bait attracts the adult flies to feed on the product, and the spinosad kills the flies. GF-120 is a prepared bait, but is only sold in gallon sized containers for at least $80. You could consider mixing your own bait solution with spinosad concentrate, and about 4 to 6 tablespoons of molasses per gallon of water applied. The GF-120 or homemade spray mix does not need to cover the entire tree. Instead, it should be applied as evenly spaced, large droplets.
News and Production Information
The fourth summer field meeting for the Northern Utah Fruit Growers (commercial growers in Box Elder, Weber, Cache, and Davis counties) was held on the evening of Wednesday, June 27, at the North Ogden LDS Church Welfare Peach Farm. The growers learned about upcoming pest issues to watch for, including an interesting explanation of Diane Alston’s research on prionus root borer. This can be a troublesome pest of cherries in sandy soils. (More about that work can be found in a past Utah Pests News article).
Much of the time was spent on the importance of irrigating trees in summer (see next article below). Dr. Brent Black explained the use of ET readings on the Utah Climate Center orchard weather data website, soil moisture meters (every commercial orchard should use them), what the readings mean, and how to interpret them. He has several fact sheets on irrigating fruit trees, and those links are provided in the article below.
USU Extension Ag Agent, James Barnhill, showed the use of “high tech” moisture monitoring sensors whose data can be downloaded to a special software program that provides precise information on when to water, and the effectiveness of the waterings. We ended the meeting by touring the orchard to learn from the manager, Bruce Liston, about the successful management practices that are conducted on the farm.
If you are a commercial grower in any of the counties listed above and are interested in attending a meeting (but do not receive the email or postcard announcements), please send us a message with your contact information. The meetings are a great way to learn about pest and production information from USU Extension, and to ask questions about your own orchard.
The next meeting will occur in September to discuss fall chores. Hope to see you there!
Content obtained from the "Orchard Irrigation" fact sheets by Dr. Brent Black and others found on the USU Extension website.
Commercial and home growers should be thinking about irrigation practices for fruit trees, especially during the time when fruit is on the tree and ripening. Drought stress will reduce fruit size or lead to sunburn or shriveling, and will stress trees so that they may be more susceptible to flatheaded borers. Stone fruits, in particular, are sensitive to water stress during the period of flower bud formation for the following year (which can lead to double-fruiting), usually in July. Over-irrigation is just as detrimental, especially in poorly drained soils.
Tree water use
How much water fruit trees use depends on species, cultivars, tree size and air temperature. Trees use water daily through updake by the roots and then transpiration from the leaves. This daily water use can be measured by evapotranspiration (ET), expressed as inches/day or inches/week, which is the amount of water evaporating off the soil surface plus the water used by the tree. ET is estimated from air temperature, relative humidity and wind speed. At full bloom, an orchard is using very little water. Water use increases dramatically until the full canopy is established, and increases again slightly (mid-season to harvest for apple, fruit ripening for peach), and then declines after harvest.
Whichever irrigation system you utilize, it is important to know how much water is being applied.
Ways to determine when to water
Soil moisture meter
Moisture blocks (WatermarkTM sensor Irrometer Co., Riverside CA) are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures relectrical esistance (about $145). The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
Tensiometers (many brands), which are less expensive, measure soil moisture tension, which indicates the effort required by root systems to extract water from the soil. Higer tension means drier soils.
How Much Water is Needed
Irrigation requirements depend on how much water your soil type can store. If you apply too much water, it percolates below the root zone, leaching away nutrients, and is never used. About 70% of water usage occurs in the upper 2/3 of the rooting zone, which is about the upper 18-24 inches of soil.
Soil moisture sensors will tell the level at which field capacity occurs. By graphing the readings from soil moisture meters over time, you can fine tune when to water and how much to use. Efficient irrigation aims to keep the readings of the sensors between field capacity and the plant’s stress point. By having the sensors at at least 2 different depths, you can determine whether you are under- or over-watering.
ET values can be used to determine how much water is needed to irrigate effectively, and how often, but requires a bit of calculation. You will need to know the following:
More on these calculations can be seen in the individual fruit fact sheets noted above.
The TRAPs website (Timing Resource and Alert for Pests), housed on the Utah Climate Center website, is a valuable tool for looking up when to spray certain plant pests. The TRAPs website provides this information for almost 60 locations in Utah. This is where we get the "when to spray" information for these IPM pest advisories. And for some pests, like codling moth and peach twig borer, we can tell how many adult moths have emerged and how many eggs have hatched per generation based on daily temperatures. That information is also included on the TRAPs website.
The steps below show how to use TRAPs, or you can view a video tutorial that explains the site in more detail.
TRAPs opens with a map loaded with red "dots" that represent weather stations in Utah. Note that the map takes a few moments to load the stations:
Using TRAPs, Step 1
Select the weather station location closest to you by clicking on a red dot on the map, or by one of the two methods explained below.
Using TRAPs, Steps 2 and 3
After you have selected your city, click on the "pest" drop down list to select the pest. Then, hit "submit" for quick access to the results page.
Using TRAPs, Alternative to Step 3
If you hang monitoring traps and determine a biofix for certain pests on your own farm, you can enter that information by clicking on "Enter your own Dates." The biofix date is the date of first moth flight, and the end date is typically the current date. This option is also useful to look at historical dates to make comparisons.
Using TRAPs, Step 4
The results page shows all data from the pest biofix/start date to the current date, plus 5 weeks of forecasted data (the first 6 days are local forecast and the remaining is from 30-year averages). For example, this table below shows that in North Holladay, on June 28, egg hatch for the second generation of codling moth is just beginning (1.3%), and that about 16% of adult moths have emerged.
Click on a row with a blue circular "information" icon to see the "Management Actions" on the right side of the table. This information tells when to start or stop sprays.
Precautionary Statement: Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed herein.