Cool to Hot update

Flea beetles are a concern on tomatoes that were set out in May before weather was settled. These plants were stunted from the cold nights and have struggled to begin rapid growth even with the last week of hot weather.

Key to overcoming flea beetle feeding is to promote rapid growth of transplants and seedlings. Flea beetles jump from the soil and attack lower leaves first (photo right). If a transplant grows rapidly as did this tomato set out June 5 (see photo left), they overcome injury. For details and control suggestions for flea beetles that infest tomato family, cabbage family and other plants, see the CSU Extension fact sheet Flea Beetles.

Cilantro flowering has promoted more questions than usual this season. The quick change from cool to hot weather caused plants to rapidly develop flower stalks. Both temperature and day length influence flowering. In hot weather during the long days of summer, cilantro rapidly produces flower stalks with ferny foliage as opposed to the desireable flat leaves (photo shows both).

Plants induced to bolt produce flowers and set seed in four to six weeks from time of sowing. If you purchase transplants, they can quickly start to flower too. Grow plants in cooler shade to delay flowering. Sow a succession of cilantro seed every few weeks through the summer to produce a constant supply of the herb. In cooler spring weather, cilantro will keep in the leafy stage weeks to a month longer.

Note that if plants go to seed, you can make coriander spice from grinding the seed instead of harvesting cilantro leaves.

Photo credit: Flea beetle injury lower tomato leaves, Tomato transplant outgrowing flea beetle injury, Cilantro - All Carl Wilson

Planting, flea beetles and children

Late May is a busy time in Front Range vegetable gardens. With Memorial Day weekend rains (3 inches in my Denver garden), weeds are growing but easy to pull. Soil is moist for transplanting tomatoes and other warm season plants into the garden. It is also the time to direct-seed warm soil requiring plants like squash, beans, corn and cucumbers.

A visit to the West Washington Park community garden reminded me of several things. The first was how much the heat island effect of city centers has on advancing the season. Their gardens are about a week ahead of gardens in the outer parts of Denver due to the warmer temperature.

Second, early season insect pests are becoming active, foremost among them flea beetle. Germinated beans were already showing holes (photo above left) and upon closer examination, the shiny hopping beetles were present (palestriped flea beetle photo below).

Not only beans but tomato family and cabbage family plants are attacked among other vegetables. Watch young seedlings closely and take action before damage becomes too extensive. While mature plants can withstand some 10 to 20 percent loss of leaf tissue with no adverse affect, seedlings are another matter.

Trap crops such as radish are one good idea. Diatomaceous earth is an effective repellent, and several insecticides including the bio-derived spinosad are effective. Weekly reapplications are often necessary as new plant growth will be unprotected and insects are very mobile. For more photos and control recommendations, see the Colorado State University Extension Flea Beetles fact sheet.

The third reminder I received from my visit is to involve children in your vegetable gardening efforts. Now that school is out, choose age-appropriate garden activities for children and youth, whether they are yours or your neighbors. They will be the richer for early involvement in the garden and receiving the benefit of your presence in their lives.

Photo credits:
Flea beetle damage on bean seedlings, Carl Wilson
Palestriped flea beetle close up, Frank Peairs, Colorado State University, Bugwood.org
Children’s toys among beet seedlings, Carl Wilson