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

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

June vegetable growing notes

Although late this year, the weather is at last consistently warm. The cold, fifty degree highs of the June 12 to 13 weekend marked the last of lingering spring and days finally yielded to warmer temperatures. Cool season vegetables are bolting (seed formation photo right) and warm season vegetables are taking off. Nighttime temperatures are out of the forties, and the fifty some degree nights are even skirting with sixty degrees F. It’s time to think about early summer vegetable gardening tasks.

Fertilize to size tomatoes and peppers – After transplants are established and growth really starts, it’s time to fertilize and encourage plants to put on size. This early growth builds the frame to bear a decent fruit load. In mid-summer fertilization should cease because you want the plants to enter a fruiting mode and not produce vegetative leaf growth.

Seed those 60 day’ers– June is the time to seed or continue to succession seed a variety of vegetables for summer. Carrots, beets, chard, collards beans, squash, New Zealand spinach, and others are all fair game. Many of these are 60 days or less to harvest.

Thin – Once seeds have germinated, do take care to thin seedlings by pinching, cutting or pulling out. Crowded plants won’t produce good yields. Seeds such as beets are really a dried fruit that contain multiple seeds and the germinated cluster of seedlings must be thinned (photo above left). Snip the plant to be removed at the soil line with a scissors to avoid disturbing the roots of the seedling meant to be left to grow. Beet thinnings can be used for salads.

Water – Consistent watering is coming into play big time. You can cut back from the post-transplant babying of plants into a more normal, twice-a-week routine (in clay soils – more frequently if growing in sandy soil). Check soil for moisture and only allow plants to get three-quarters dry before watering. Note that many people overwater tomatoes according to national studies.

Mulch – Now that temperatures are in the nineties and soils are thoroughly warm (68 degrees F at last check), mulching should be considered. Herbicide-free grass clipping mulch is my favorite (photo right). It’s readily available on a weekly basis with lawn mowing, quickly biodegradeable when it’s eventually mixed into the soil, and performs all the usual mulch chores of keeping down weeds, holding in moisture, keeping soil surface temperatures cooler for root functioning, etc. Apply in two installments 5 to 7 days apart with each fresh layer being no more than 1 to 2 inches thick to avoid matting, rotting and associated odors. The total cumulative mulch depth should be no more than 2 or 3 inches thick.

Photo credit: Bolting lettuce, Beet seedling clusters, Grass mulch – All Carl Wilson

Year of added fruit tree maintenance

In many years untimely freezes leave fruit trees with little or no fruit on the tree. Not this year. Even though the first half of May was cool and had two more days than normal below freezing (7 total), the temperature on those coldest nights only dropped down to the 28 degree F limit during bloom and early fruit formation.

Limit because 28 degrees F is the lowest temperature that fruit trees generally can withstand before damage to the crop occurs. This year proved that right as there are bumper crops of most fruit including apricots, peaches, cherries, plums, pears and apples.

With a heavy fruit set come responsibilities. June is a good month to consider fruit thinning if the tree hasn’t taken care of this itself through the “June drop.” Peaches, apricots and apples should be thinned to 6 inches apart on the limbs when fruit is thumbnail sized. The photo right shows peaches in need of thinning (this should have been done when they were smaller). With apples, and pears this prevents codling moth worms from traveling between snuggled fruit and damaging two apples instead of one (photo below left).

Thinning helps fruit grow to a larger size and avoids later limb breakage from too heavy fruit loads. Cherries aren’t generally thinned. Be sure not to remove the spurs (short bearing stems) when you thin the fruit on pears, plums (not always thinned) and spur-type apples. Peaches bear directly on twigs with no spur involved.

For codling moth control to prevent wormy apples in apple and pear, thin fruit, trap insects and time insecticide applications appropriately. Insecticide applications should have begun right after petal fall. Permethrin and carbaryl (Sevin) are the most common homeowner treatments which are generally timed for 10 to 14 day intervals.

Click on this link for information on dealing with apple and pear insects.

Look here for information on managing peach tree borer, the most destructive insect of cherries, peaches and plums.

Photo credit: Heavy peach set, Apple cluster - both Carl Wilson

Pruning grapes

It’s tough to answer a question from homeowners on how to prune the American grapes we grow in this area. The first roadblock is their mental picture of California grape vineyards with spur-pruned grapes trained to a head or cordon. This isn’t the way American grapes should be pruned.

American grapes don’t produce fruit next to the main trunk. Instead of European wine grape-style pruning to 2 or 3 buds, we leave 6 to 18 buds because of the vigorous American vines. The more vigorous the variety such as ‘Concord’, the more buds can be left.

The second dilemma in answering the how to prune question is that vines are usually already sprawled over an arbor or pergola. Making any sense out of vine structure and counting buds isn’t realistic at this point. I advise the “clear dead canes out and prune live canes to keep the vine on the arbor approach.”

With the vigor of these American vines, pruning wrong is awfully hard to do because rank growth will take care of any pruning “mistakes” if there is such a thing. The real mistake is not doing any annual pruning at all. In some form this usually meets the two real viticultural pruning objectives of shaping vines to meet gardener’s needs and balancing fruit production with vegetative growth.

The vines shown in the photo top left contained dead canes from the previous season. They were recently pruned to remove dead wood and clear the way for this season’s growth (obviously well along). Two varieties are grown on this arbor, ‘Concord’ and ‘Himrod’. The two “after” photos right show the arbor after pruning and the amount of dead wood cleared out.

What are your thoughts about how to prune and the harvest results you’ve gotten with your method? Please tell us where you live and what grape variety you’re growing.

Photo credit: All 3 photos Carl Wilson.

Warm season finally arrives

Whew! It was great to finally get the transplants off the porch and into the garden on Memorial Day weekend. Even then nighttime temperatures were only high forties – still a little cold for tomatoes and peppers.

The first half of May was very cool in Denver. Although it didn’t freeze past the average last frost date of May 10, the nights were cold. People wanting to transplant early had to provide season extenders such as water walls for nighttime heat.

Those transplanting without season extenders once again proved the wisdom of waiting two to three weeks past the average last frost date. Only by then had the weather settled and cold winds turned warm. I had questions about why peppers and tomatoes weren’t growing from people transplanting early in the month. The answer is cold nighttime temperatures under 50 degrees F.

Now it looks like daytime temperatures will reach close to 90 degrees F with nighttimes in the low 50’s – perfect for warm season vegetables. This is typical of our high and dry steppe climate, going from cold to hot in a short period of time.

Continue to seed those 60 day root crops. Even though beet seed is larger than carrots (photo), I use germination fabric over both to keep the seedbed moist and increase germination percentage. It’s a great tool particularly on 90 degree F days when soil dries out so fast.

Photo credit: Protecting transplants, Transplants in garden, Beet seed - all Carl Wilson