This “CAUTION” post is similar to one I made a few weeks ago for cole crops; a quick way to highlight a potential problem, in hopes that consultants, gardeners, etc., will do some scouting to investigate if/to what extent they may be affected.

We saw, for the first time this season, some western striped cucumber beetle (Acalymma trivittatum) activity on both both weedy volunteer and cropped cucurbits.

This pest is of particular concern because it vectors bacterial wilt, a plant pathogen caused by Erwinia tracheiphila bacteria. Researchers now suspect that, rather than overwintering in the intestinal tract of adult beetles, the bacterium overwinters in the sap of alternate host plants (i.e. volunteer and weedy cucurbit species). The alternate host plants may not show symptoms of being infected, which can make management difficult.

As adult cucumber beetles feed, the beetles become infected with bacterial wilt, and then transmit it to crops. This infection can be direct (feeding on one host then another), or secondary (fecal contamination of already wounded tissue). Once the disease is established, it cannot be managed with pesticides, so ‘awareness’ of cucumber beetle activity levels, and subsequent control if necessary, is considered the best preventative tactic.

A few tips for scouting bacterial wilt in cucurbits:

    • Melons, squash, and cucumber are considered more susceptible than zucchini and watermelon, but all related plants (Cucurbitaceae) are at riska
    • Damage can occur quickly – scout 2-3X/week for beetle pressure and wilt symptoms
    • Symptoms can be immediate on some plants, and not occur until after fruiting on others
    • Leaves may look dull green, yellowing at leaf margins
    • Vines wilt during the day, but seem to recover at night
    • Quick diagnostic test (photos below): stems/vines are cut close to the crown, and a ‘stringy’ sticky substance appears when the two halves are pressed then pulled apart from each other. b
erwinia_knifecutting
1. make a clean, vertical cut close to the crown
2. push segments together then slowly pull apart

PHOTO CREDITS: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

 

 

There is a great new eXtension article about biology and management of cucumber beetles in organic farming systems available at: https://beav.es/ZYJ (it’s ok – we’ll use a Beavs shortlink to promote WSU just this once…there’s some great people/research going on up there!)

 

aDISCLAIMER: regional differences in pathogen expression are likely, do not rely on literature from other areas
bDISCLAIMER: may not work for all species or all cases

 

If you read this title and wondered “where are weeks 1 thru 6?” .. you need to subscribe! Weekly reports are sent directly by email, but sometimes there is so much happening, I have to do a mid-week update via blog. This is one of those weeks!

  • The cabbage looper outbreak continues, with trap counts averaging 1000 times higher than normal. Yes, you read that right.
  • 12-spot beetles. You see ’em, you know ’em, but did you know they can be devastating underground pests? The pictures below were taken this week on spinach for seed and seedling spinach (yes, there’s a difference).
    • As adults, beetles chew on foliage, flowers, fruit, corn silks, etc.
    • As larvae, grubs chew on and tunnel through roots.
    • For more info about 12-spots, click here; or branch out a bit and learn about the whole rootworm complex that plagues regional growers and gardeners.

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WEEK 23 –
WEEK 23 – Corn earworm flights have been consistently high, and scouting this week revealed late stage larvae, pupal exit holes, and newly-emerged adults that will lay eggs within 3-5 days. This diversity makes control difficult, and scouting is recommended. Spotted cucumber beetles do become active in the fall, but levels this year are about 500% higher than historical norms.

Read the full report here: http://bit.ly/VNweek23 and subscribe on our homepage to receive weekly newsletters during field season.

Western Corn Rootworm (WCR) is considered the most important corn pest in the U.S.1 . Most of this damage occurs in the Midwest, where corn acreage dominates the landscape. Over the last 50 years, farmers have used cultural, genetic, and chemical control strategies to lessen the effect of WCR and protect yields.

In comparison, the PNW produces a very small amount of corn (<5% of all regional farmland). Therefore, western corn rootworm has not been a problem for us so far2, and growers are much more accustomed to 12-spots (which is a western variant of the southern corn rootworm – confused yet?!)

Life histories are similar: larvae chew on roots, adult beetles attack foliage and can clip silk if populations are high enough. This interferes with pollination and can lead to poor tip fill.

poor tipfill of corn
Poor pollination during silking affects tip fill. This picture is from the Midwest, where WCR is a much bigger issue than it is in the PNW. PHOTO CREDIT: J. Obermeyer

 

Q: So why mention WCR if it’s not yet a problem here?
A: This species is worth monitoring because it has been moving westward for the past 10+ years, and could become more abundant if corn production increases in the PNW. Yellow sticky traps are great passive sampling tools for many pests, so in short…might as well.

Expansion of WCR in 10 years. Based on C.Edwards and J. Kiss (Purdue Field Crops IPM) and A. Murphy (OSU, PNW 662)

RESOURCES:

  1. Gray, M. E., Sappington, T. W., Miller, N. J., Moeser, J., & Bohn, M. O. (2009). Adaptation and invasiveness of western corn rootworm: Intensifying research on a worsening pest. Annual Review of Entomology 54: 303-321.
  2. Murphy, A., Rondon, S., Wohleb, C., and S. Hines. (2014). Western corn rootworm in eastern Oregon, Idaho, and eastern Washington. PNW Extension Publication 662. 7 pp.
WEEK 16 – Two types of rootworm are now widely present in the Valley. See this page to learn how to ID and differentiate between them. Another, third species, may be on its way. Western corn rootworm has been moving westward since 2004.

Read the full report here: http://bit.ly/VNweek16 and subscribe on our homepage to receive weekly newsletters during field season. Thanks!

WEEK 15 full report available here:

  • Black cutworms will be large now, and can cause major root damage in corn. Consult the PNW insect management handbook for possible rescue treatments.
  • Diamondback pressure is still very high at remaining production fields.
  • Corn earworm – If chemical controls are needed, they must be applied before larvae move into developing ears.

WEEK 14:

    • The 2nd generation of 12-spot beetles has emerged, and activity will likely remain high through September. Sweep fields with a sweep net to accurately assess population levels. Take a minimum of four samples (ten arcs of the net per sample) from different parts of the field. Beetles tend to concentrate on field edges. At this time of year, adult beetles are pests within snap bean and squash fields. They feed on folliage and developing pods.

     

    • There has been a boom of adult diamondback moths detected in pheromone traps. Development will be rapid under warm temperatures. Intensify field scouting so that treatments can be applied to avoid contamination.

    Read the full pest report HERE and subscribe to receive alert updates.

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WEEK 7:  Flea beetles above, rootworms below, loopers everywhere

Let me explain:
  • Flea beetles invade fields rapidly, and can cause substantial damage to newly emerged leaves. Scouting is simple, thanks to the characteristic leaf damage. See photos and learn more here.
  • Rootworm is the common name for larval Diabrotica beetles. They feed underground, but can be distinguished from maggots by the presence of thoracic legs and a brown sclerotized plate just behind the head.
Rootworm. PHOTO CREDIT: Ken Gray, OSU
  • Cabbage Looper moths continue to be very abundant in the landscape. There is no diapause in this species, so 6-7 generations per year are possible if environmental conditions are suitable. Although trap counts are way above normal, the effect on crops has yet to be determined, and depends on a variety of factors. We will be discussing some of these in the weeks to come.

Read the full pest report HERE and subscribe to receive alert updates.

WEEK 4: Moth movement is low, rootworms in the landscape.

Don’t worry if you’re getting a late start to the planting season. So are the bugs. Many of the pest moth species we track are LOWER than normal for this time of year.

You may start to notice those familiar 12-spot beetles around, particularly on the dandelions in your yard or garden. These are the overwintered females, looking for suitable egg-laying sites (seedling corn, cucumbers, beans).

Check out this week’s full report HERE, and subscribe to receive VegNet highlights straight to your inbox!

**Thanks for your patience as I continue to build the rest of this site**