Beneficial insects aid in controlling spider mites ByDennis Pollock Six-spotted thrips are an almond grow- er’s best friends. Why? avoid loss of those natural enemies is to treat if neededwithamiticide that doesn’t kill beneficials, he said. leaves are infested and you capture no thrips, or if you plan on killing thrips,” Haviland said.
to focus on hot spots—including edges and the crotches of the tree—prior to July 1. Focus on leaves, randomly choosing 15 leaves per tree on at least five trees. Then, hesaid, count thenumberofmitesand the number of predators. Yellow strip traps should hang in orchards for oneweek. There is a close relationship between the ebb and flow of thrips and mites. Treating too early can “starve predators,” Haviland said, whereas treating too late can risk defoliation. “Moni tor ing mi tes tel ls you how many mites there are,” Haviland said. “Monitoring thrips tells you how many mites therewill be.” As the thrips-to-mite ratio nears zero, the mite population increases exponen- tially, he said. As the thrips-to-mite popu- lationapproaches infinity, themite popu- lation decreases exponentially. FormakingMay treatment decisions, he advisednot totreatunless40%of leavesare infested. The “no-need-to-treat decision” is confirmed if there’s one thrips per card. “May sprays are only needed if 40% of
When treating formites, it’sbest todrive no faster than 2miles per hour and apply between 100 and 200 gallons per hour, he said. The fan speed should be enough to displace air in the tree but not to blow product through to the next row. He rec- ommended toconsider air inductionnoz- zles for higher elevations in the tree. Todetermine if andwhen tomakeahull split spray,Havilandsaid, if thereare fiveor six thrips per card, “walk away.” A new resource available from the Almond Board describes almond or- chard pests, steps to improved irriga- tion and how to avoid pesticide drift. A free copy may be obtained by emailing fieldoutreach@almondboard.com. Forms to be used for orchardmonitor- ing are available at ipm.ucanr.edu/PMG/ C003/almonds-mites.pdf. (Denni s Pol lock i s a repor t er in F r e s no . He ma y b e c on t a c t e d a t agcompollock@yahoo.com.)
Among beneficials is theWesternpred- atorymite, which is teardrop-shaped and clear to red. Haviland said it can complete a life cycle in seven days and can provide complete control of spider mites. It often arrives late, because it has no alternative food source in the spring. There’s also the spider mite destroyer, which consumesmany eggs or a half doz- enmitesperday. It grows fromegg toadult in about three weeks in warm tempera- tures. Females typically live one to three months, during which they lay about 100 to 200 eggs. Like the predatory mite, Haviland said, “it is known for showing up late in the game.” Green lacewings and theminute pirate bug are other predators. The six-spotted thrips feeds almost ex- clusivelyonspidermitesandthrives inhot, dryclimates. It caneat 50eggsperday, and thethripspopulationcanquadruple inone week; it is cannibalistic if food is scarce. Ninety percent of the thrips population are females, and populations of thrips can double every four days. Haviland said thripshavereplacedpredatorymitesas the dominant natural enemy of spidermites. Whensampling for spidermites, he said
They love to eat spider mites that cause stippling on the leaves of almond trees, which can result in loss of leaves and re- duction in photosynthesis. David Havi land, a Univers i ty of California farm advisor in Kern County, delivered thatmessageduringanAlmond Board of California webinar, in which he talked of the importance of monitor- ing both the pests and their foes to avoid sprays that could kill beneficial insects. Hedescribedhowto identify thePacific spider mite, which overwinters as orange females in leaf litter and crotches of the tree. The pest moves to the lower canopy in mid- to late March and takes on a tra- ditional color. Themites feedexclusivelyonleaves, can complete a life cycle in one week and are associatedwithwebbing. Their impact on photosynthesis can bring reduced yields the following year. The good news is that almond trees are very resilient,Havilandsaid, andcanwith- stand the loss of some leaves. Conditions that promotemites include tree stress, dust, and lack of natural ene- miesoruseof pesticides that caneliminate the enemies that are out there. Oneway to
Wintertime farmland flooding appears to help drinking water
recharge groundwater. Ifrelativelycleanmountainrunoff isused, Dahlke said, thewater filteringdown to the aquifer could also clean groundwater that hasbeenaffectedbynitrogenorpesticide. A map developed in 2016 by UC Cooperative Extension specialist Toby O’Geenidentified3.6millionacresof farm- land with the best potential for managed aquifer recharge, based on soil type, land use, topography and other factors. Now, Dahlke and colleagues have analyzed the map, finding nearly 3,000 locationswhere floodingsuitable farmlandwouldrecharge water for 288 rural communities. “If we have the choice to pick a location where recharge could happen, choose thoseupstreamfromthese communities,” Dahlke said. Shesaidshebelieveswintertimeflooding for groundwater recharge can help water districtscomplywiththestate’sSustainable GroundwaterManagement Act. “Wehave todoanythingwe can to store any surplus water that becomes available to save it for drier times, and our aquifers provide a huge storage for that,” she said. Dahlke’s lab collaborates withUC farm advisors and specialists and with scien- tists at other UC campuses to learn about the agronomic impacts of flooding a va- riety of crops, including almonds, alfalfa and grapes. UC said the lab’s groundwater banking project plans more studies in groundwa- ter basins across the state, to learn more about suitable locations, technical imple- mentation and long-termoperation. The scientists alsoplan toaddressoperational, economic and legal feasibility of ground- water banking on agricultural land.
Using farmland for wintertime aquifer recharge could help nearby communities replenish their groundwater supplies, ac- cording toUniversityofCaliforniaresearch showing thatnearly300rural communities could benefit. The research is part of ongoing work to determine how flooding farmland in the winter could refill underground wa- ter supplies. HelenDahlke, a professor at UCDavis, has been evaluating ways to flood ag- ricultural land when excess water is available during the winter, in order to
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10 Ag Alert May 26, 2021
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