California Fruit and Vegetable

Tag: University of Arizona Extension

  • Summer Sanitation is Important as Ever

    It is never too early to start planning for next produce season, particularly with the threat of Impatiens Necrotic Sprot Virus (INSV) looming. As many of you know, INSV was found in several Yuma locations this spring, particularly in the Tacna area. Overall, INSV incidence was very low (~1% incidence), but there were a few fields where incidence was estimates at > 25% (see Chart 1 below).

    With desert lettuce production now finished, the question remains; will INSV in these infested areas survive the summer in the absence of lettuce. Of course, this depends on the availability of host plants in the cropping landscape to serve as reservoirs for INSV in the next 4 months, as well as the abundance of western flower thrips on these hosts. A team of applied scientists at the UA Yuma Ag Center –Bindu Poudel, Stephanie Slinski, Barry Tickes, Marco Pena and myself (with the assistance of Daniel Hasegawa, USDA-Salinas) – are currently trying to determine this.  First, we know that many of the common weeds currently found in drainages, field borders, and ditch banks serve as reproductive hosts for western flower thrips.  What this means is that thrips are capable of colonizing these weed hosts. Immigrating adults can transmit viruses and larvae can acquire viruses that can be transmitted after they emerge as adults. Recent areawide monitoring of crops and weeds in Tacna and Yuma Valley showed thrips adults and larvae were abundant on nettle leaf goosefoot and cheeseweed (see Chart 2 below), and more importantly, tissue samples recently collected from weeds near previously infected lettuce fields in Tacna tested positive for INSV in nettleleaf goosefoot, cheeseweed, and purslane.   It appears that these weeds could provide a green bridge for the virus and the vector from now till September. The threat of INSV surviving within our desert cropping system in the absence of lettuce this summer is real.

    So, weed management this summer is going to be very important if we hope to eliminate the local presence and spread of INSV.  Growers should be extremely vigilant in keeping ditch banks and low-lying drainages adjacent to fields free of weeds. When upcoming wheat harvests are completed, all weeds along field edges need to be thoroughly disked under along with the stubble.  Even a few remaining goosefoot or purslane plants on a field edge can potentially harbor INSV and a significant number of thrips vectors. Similarly, periodic disking of alfalfa borders and field edges should help minimize weed regrowth.  Same goes for cotton and Sudan grass fields. When spring melons are harvested, growers should promptly disk under plant residue.  Any PCA watching melons this spring can attest to the attractiveness of melon flowers to thrips. Finally, as growers start to flat water fields in preparation for fall lettuce planting, it will be as important as ever to promptly control weeds emerging in those fallow blocks. Remember, recent weed sampling showed purslane tested positive for INSV, and a ten-acre field infested with purslane can potentially generate a lot of thrips. So can volunteer melons.  Thus, summer sanitation is as important as ever. Bottom line:  anything growers can do to reduce weed abundance in and around their fields can only help. For more information on this crop sanitation, please visit Weed Interference with Insect Management in Desert Crops.  The other critical question we are working on is whether our summer crops (alfalfa, cotton, melons) serve as hosts and reservoirs for INSV. We do not know yet, but our team is working on it.  We’ll let you know when we know. — John Palumbo, University of Arizona Extension

  • Whitefly Management on Spring Melons 2021

    Now that the produce season is essentially finished in Yuma, it is time to move into melons.  Spring melon crops are rapidly growing, and so are insect pest populations. Cabbage loopers and leafminers are becoming evident in some areas, and PCAs should start ramping up their monitoring and sampling. More importantly, whitely populations are quietly becoming abundant on the spring melons of all sizes. Adults can easily be found on recently planted melons located at the Yuma Ag Center, and reports from local PCAs suggest that adult populations are beginning to show up on older plantings. As temperatures increase and crops/weeds mature, avoidance of excessive feeding from whitefly nymphs should be the primary concern on all melon types. Although CYSDV does occur in later spring melons, it is rarely yield limiting. But honeydew and sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability is whiteflies are not adequately controlled.  Our research has shown that to prevent fruit yield and quality losses on spring melons, a foliar insecticide treatment should be applied on threshold; that is, when leaves have greater than 2 adult whiteflies per leaf, when averaged across an entire melon field. At this level of adult abundance, immature populations are just starting to colonize, and timing sprays based on the adult threshold has been shown to significantly reduce the chance of yield / quality losses during spring harvests.  This threshold applies for the use of recommended IGRs (Courier, Knack, Cormoran, and Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion), neonicotinoid-like compounds (Sivanto prime and Transform), diamides, (Exirel and Minecto Pro) and the new feeding disruptors (PQZ and Sefina).  For more information on whitefly management and available insecticides, go to these documents on IPM and Whitefly Management  and  Whitefly Control Options-Spring 2021.     Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine bee safety of a product before making an application in a melon field.  If applications are necessary during bloom, only apply a product that is considered bee safe (e.g., PQZ, Sefina, Sivanto, Assail). We also recommend that insecticides only be applied when honeybees are not actively working in the field (e.g. 10:00 pm – 3: 00 am). — John Palumbo, University of Arizona, Yuma College of Ag & Life Sciences

  • Late-season Thrips Management in Lettuce

    Effective control of western flower thrips (WFT) to prevent cosmetic scarring and contamination is important in spring lettuce crops, and now that INSV has been found infecting plants in Yuma lettuce, management becomes even more important.  For most of the growing season, WFT numbers have been below average based on sticky trap counts, field reports and population densities here at YAC. However, in the past few weeks WFT populations have increased in most growing areas. This is not surprising as we typically observe “bioconcentration” of WFT during March and April on late lettuce as surrounding produce acreage declines. Each time a lettuce field is harvested, and disked, adult thrips disperse from these areas into the next available lettuce field.  As the number of lettuce acres becomes reduced near the end of the season, this creates a bottleneck effect that concentrates high numbers of thrips adults on the remaining fields under production. This can often make chemical control of WFT very difficult, particularly in March, as adults can continually re-infest fields following spray applications.   So, what management approaches can you take to manage thrips and hopefully reduce the potential incidence of INSV.  The first line of defense should be sanitation. Growers should disc under produce crops immediately following harvest. The longer a harvested crop remains above ground, the more insects that can build up and move to adjacent lettuce fields, especially with the dry, windy, and warm weather we typically have in March.   If only light INSV incidence is present in pre-harvest fields, PCAs should consider rogueing and removing suspect plants from the field.  Ultimately, this may curb secondary infection within the field. 

    Controlling WFT with insecticides is the best approach to minimizing cosmetic feeding damage and may reduce spread of INSV within fields. For adults, which can easily be found on the leaf surface, your best choices of insecticide are methomyl (Lannate) or acephate at a high label rate.  They are the most efficacious products against adult WFT. Radiant is not as consistently efficacious against adults, but a 7 oz or higher rate will provide the best knockdown and residual control of WFT larvae.  Remember, the key to preventing cosmetic damage by WFT is to maintain larval populations at low levels.  The cryptic or thigmotactic behavior of thrips often makes them difficult to find on lettuce plants. Research has shown that if you can see a few adults and larvae on the plant, it means that there are likely 10-fold more thrips actually on the plant (hiding near the base of the plant between midribs).  This behavior also means that spray coverage is important, particularly with contact insecticides like Lannate. There are other insecticides such as Torac, Minecto Pro, Exirel, Movento and Assail that can provide suppression (50% control or less) against WFT larvae, but don’t expect much activity against adults. For more information on the identification, biology, ecology, and management of thrips on desert produce please visit Western Flower Thrips Management on Desert Produce. — By John Palumbo, University of Arizona Extension