Wednesday, July 28, 2010

More butterflies than usual?

Is it just me or are many of you seeing more butterflies than average this summer? I also think I’m seeing fewer European paper wasps, a major predator of butterfly larvae. Perhaps that’s why.

The adults and larvae of butterflies require different food plants. The larvae of cabbage worm eat cabbage family plants (photo of damaged kale left, larva photo right). The white adult butterflies gather nectar from a variety of flowering plants (adult on thistle below left).

Control of cabbage worm includes the use of the natural bacteria Bacillus thuringiensis Kurstaki strain. See the CSU Extension fact sheet on Bacillus thuringiensis for advantages and disadvantages of using this natural control. Another idea is to exclude the adult butterfly from laying eggs on plants with the use of a floating row cover (photo right).

A colorful butterfly plentiful throughout the Denver area this season is the Two-tailed swallowtail. Adults (photo left) feed on geranium, thistle and milkweed plus other flowers, larvae (photo right) consume green ash and chokecherry. Gardeners curious about the yellow butterflies flying by can now rest easy knowing the larvae are not eating their vegetables.

To learn names, see photos, and find out the food plants for the adult and larval stages of common Colorado butterflies, see the CSU Extension fact sheet on butterflies in the garden.

Photo credit:
Cabbage worm damage to kale, Carl Wilson
Cabbage worm larva, Whitney Cranshaw, CSU Extension
Adult cabbage worm butterfly, Davud Cappaert, Michigan State University
Row cover, Carl Wilson
Two-tailed swallowtail adult, CSU Extension
Two-tailed swallowtail larva, Whitney Cranshaw, CSU Extension

Thursday, July 15, 2010

Seed now and watch for cutworms

Now is the time to plant seeds of late summer and fall crops where earlier ones have been harvested. Chose 60 day or less crops (carrots, beets, bush beans, radishes, Swiss chard, New Zealand spinach) or ones that like to mature in cooler temperatures (lettuce, peas, spinach, kale, collards, Asian greens). Note that a nice option with greens is that they can be harvested at almost any stage of maturity in the event of a short growing season.

With a temperature in the nineties F, small seed will be hard to germinate Use seed germination fabric and water lightly but frequently.

One seed germination hazard that some people think is a spring but not summer pest in cutworms. Cutworms are caterpillars that cut and kill tender seedlings round the soil line.
The notorious "miller moth" that people in our area recognize in the adult flying form (photo above left) is Army cutworm in its larval caterpillar stage. (See above right photo).

Note that there are also climbing cutworms as the person who brought chomped basil leaves in for diagnosis today discovered. Beet armyworm (see photos adult left and larva right) is a climber active in mid to late summer that chews on a very wide variety of plants. Variegated cutworm is another (photos below).

Cutworms typically feed at night and hide in soil cracks, under dirt clods or seek other cover during the day. If you are going to find them, you have to go out after dark with a flashlight.

Cutworms are preyed upon by ground beetles, rove beetles, spiders, tachinid flies, parasitic wasps and other garden insects as well as toads and snakes. If natural enemies aren’t providing sufficient control, consider your weed situation. Cutworm moths are attracted to weeds for egg-laying.

Promote rapid seedling growth with good cultural practices (right amounts of water, loose soil, proper planting times, etc.) and use transplants. Transplants and older plants aren’t as tender and less likely to be damaged at the soil line. Note that climbing-type cutworms will find the tender leaves on top.

Protect tender transplants and seedlings with cutworm collars (cardboard, foil) or milk carton rings. Insecticide baits are available for cutworms. They are more targeted than whole-plant sprays which may kill beneficial insects as well as pests. Note that B.t. (Bacillus thuringiensis) natural insecticide is generally ineffective against cutworms.

Photo credit: Miller moth Whitney Cranshaw, CSU Extension; Army cutworm larva Frank Peairs, CSU Extension; Beet armyworm adult Merle Shepard & Gerald Carner & P.A.C. Ooi; Beet armyworm larva Frank Peairs, CSU Extension; Variegated cutworm adult Ian Kimber; Variegated cutworm larva Charles Olsen, USDA APHIS PPQ.

Friday, July 9, 2010

Mind the herbicides

Use caution in using herbicides because injury to vegetable gardens is always a concern. Common ways herbicides reach vegetables are vapor movement from nearby properties, drift of sprays and through imported manure or straw mulch.

Growth hormone type herbicide injury causes leaf feathering, cupping, stem twisting and sometimes produces compressed growth resembling a cobra’s head (also called fiddlenecking). Tomatoes (see photo left) are particularly susceptible but other vegetables can also be affected (eggplant photo right).

2,4-D is commonly used for spraying dandelions and other broadleaf weeds. Ester forms are more likely to vaporize and be carried by wind than amine forms. Vapor clouds can drift for surprising distances depending on weather conditions. Granular formulations rarely volatilize.

High temperatures above 85 F during or immediately following applications increase the possibility of vaporization. Spraying earlier in spring, during cooler periods in summer and at cooler times of day is recommended. Follow label directions dealing with temperature.

Sprays should be adjusted so droplet size is large because fine sprays have a greater potential to drift. Use lower pressures or sprayers with large orifice nozzles that increase the average droplet size. Mind wind movement and chose calm days for spraying. Use spray shields when using products such as glyphosate (Roundup and other brands) near gardens. Do not apply insecticides with a sprayer used for weed killers.

Another way herbicides can reach vegetable gardens is in residues on straw used for mulch or through manures dug in as soil amendments. Clopyralid can be moved this way. This herbicide is not used for broadleaf weed control in landscapes but is used in pastures, crop production and rights-of-way among others.

Clopyralid is very persistent in manures, composts and soil. It can damage sensitive vegetable plants in extremely small amounts. Sensitive plants include those in the bean family (beans, peas), sunflower family (lettuce, endive, globe artichoke), and especially the tomato/potato family including eggplant and peppers.

Know your source or try imported straws and manure on a test plant in a pot before using in your whole garden.

Photo credit: Tomato and eggplant herbicide injury - both Carl Wilson

Friday, July 2, 2010

Tomato-potato psyllids watch

Psyllids are insidious insects that cause a plant condition known as psyllid yellows, the result of a toxic saliva injected by the insect. Be on the lookout for these insects on your tomatoes and potatoes now.

Insects are reported to be heavy in the Arkansas Valley and adults have been found in sweep nets in Fort Collins. Psyllids do not overwinter in Colorado and migrate from overwintering sites in southern TX, AZ and NM. Reports from the southern part of the state are tip offs to be on the watch for them. Outbreaks are erratic depending on winds and weather conditions. They can also be transported on transplants.

Watch for the eggs and nymphs. Eggs are small (one-thirty second inch), orange-yellow and supported by small stalks. Beneficial lacewings have similar eggs but are larger, white and on longer stalks. Psyllid eggs take 6 to 10 days to hatch into nymphs.

The nymphs look like flat plastic discs attached to the backs of leaves or on stems (photo above right). They are yellow at first but become green and well camouflaged as they mature. The nymphs don’t move once they settle down to suck plant juices. They excrete small, waxy beads of white “psyllid sugar” (photo left) as they feed for 2 to 3 weeks.

The adults are rarely seen and are green at first but rapidly turn dark Adults fly to new plants to lay eggs and 4 to 7 generations are produced in a growing season.

Symptoms on potato and tomato plants are similar. Yellowing or purpling along leaf midribs and leaf edges is concentrated in top leaves. As the disease progresses, the yellow-green or purple-red color spreads to the entire top growth and growth slows. New top leaves often remain small and tend to stand upright giving the top an almost feathery appearance.

When psyllids attack tomato plants early, effects can be so severe that little fruit is set. Infestations later in the growing season on larger plants cause only a small yield loss. If psyllids attack potatoes before tuber set, many small tubers form. Later attacks reduce growth and cause irregularly-shaped potatoes that may sprout prematurely underground before harvest.

Because insects are small and don’t attract attention due to being stationary and camouflaged, they go unnoticed before the damage is well underway. Watch on a regular schedule for psyllid sugar and turn leaves over to look for nymph “discs” (photo right). If found, take action right away.

Do all you can (fertilize and water regularly) to get plants growing vigorously early. Insecticides labeled and available to homeowners are permethrin and esfenvalerate products. An alternative is sulfur dust if leaf undersides can be coated. Two percent insecticidal soaps provide useful if more erratic control.

Psyllids infest but cause insignificant damage to other vegetables in this same family, eggplant and peppers.

Photo credit: All photos Whitney Cranshaw, Colorado State University entomologist