COLUMN: Striped cucumber beetle spreads virus in local gardens

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By Jeneen Wiche

I continue to stand by my belief that my best defense in the garden is me. In the morning, I go out and inspect my garden and smash insects and pick off diseased foliage, careful not to spread it to other plants by my own hand. I watch for the beginning of any abnormality and nip it in the bud. However, sometimes things slide by undetected, plus it is hard to determine bacterial brown spot from mosaic if you are not sure what you are looking for.
Some of the most common problems faced by our favorite garden vegetables can be treated easily, others spell doom. If we can note accurate symptoms, we can take steps to get rid of the problem or at least control it. I am noticing some sketchy looking green beans and some suspicious wilt among the cucumbers.
I like to grow pole beans because they don’t take up as much space and they are easier to pick; however, my very favorite bean is a French filet bean called ‘Tavera’ that is a bush type. The vertical growth of my ‘French Gold’ allows for good air circulation which cuts down on problems with rust, mildew, aphids and spider mites. But, the bush type is showing signs of some rust spreading throughout. A fixed copper fungicide can slow the progress but I will typically remove the most infected plants to offset the spread throughout instead.
Bean mosaic is a little more threatening to the bean plants. If the foliage appears to be stunted, with raised brown splotches along the central vein and the leaves pucker and curl around the margins, then you likely have bean mosaic. The plant’s growth and bean production is compromised and you might as well pull it up and destroy the debris.
More common and less problematic for beans is bacterial spot which first appears as yellow flecks on the leaves, changing to irregular shaped brown spots. Simply remove infected leaves as they appear to prevent the spread.
Mexican bean beetles and bean leaf beetles can cause the decline of bean plants because they not only chew on leaves and pods but the developing larvae feed on roots and stems, weakening or killing the plants. The Mexican bean beetle looks like a copper-colored ladybug with 16 black spots.
They skeletonize foliage as they feed, creating a lace-like effect. Apply a pyrethrin-based biological control to kill adult beetles and use summer horticultural oils to smother eggs and larvae of additional generations (usually four each year).
Like my beans, I select vining varieties of cucumbers so that I can grow them vertically, too. I find that mildew is greatly reduced; however, air circulation doesn’t keep the cucumber beetle away. Considered public enemy #1 of the cucurbit family (cucumbers, summer and winter squash, melons...) the cucumber beetle, both spotted and striped, is a chewing insect that spreads disease. It is especially troublesome because it spreads mosaic viruses and bacterial wilt, both of which have no remedy.
Mosaic viruses can infect plants anytime because the disease winters over in perennial weeds and is spread to your cucurbits by aphids or cucumber beetles. If the plants are healthy and the fruit is at least half grown, it will not affect the quality; infection earlier in the season distorts, stunts and discolors foliage and causes the fruit to taste bitter and tough.
Bacterial wilt on cucumbers is characterized by a few leaves on a plant wilting and eventually dying; fruit stops maturing and shrivels up. Cucumber beetles carry the bacteria in their mouths and infect the plant as they feed.
A sure way to confirm bacterial wilt is to cut open the stem of a wilted leaf, squeeze the sap out, and if you see a white substance,ß touch your knife to it and see if it oozes out in a fine thread as you draw the knife away....this is the bacteria. The beetles need to be controlled to avoid bacterial wilt since there is no other treatment.  Try a combination of neem oil and pyrethrin for cucumber beetles.