DOG DAYS DILEMMA

By Martin Král

Ever since retiring, the summer days here have been enjoyed by hitting the hammock as the stream of worker bees heads to their jobs. They call these early August days the Dog Days. Sirius, the bright Dog Star, fades on the southern horizon while the sun rises.

Just as the bulk of buds emerge from vigorously growing dahlias, the attention in the garden shifts from excitement to concern. The daily exercise of counting blooms (my spouse has an annoying practice of notifying me daily how many plants are showing color) also forces me to pay attention to every bush during watering to observe insect damage and infestations. In dahlias, particular diligence is necessary to deter aphids from establishing colonies, since the peduncle’s bend below a bud can hide such emergent pests. What alerted me to their arrival this time was the presence of tiny ants, quickly running up and down the stem. The ants savor the sweet liquid called honeydew that aphids produce, and this symbiotic relationship - the ants not only ‘farm’, but also protect their suppliers - encourages the spread of aphids in the garden. But aphids also can transmit viruses, and their honeydew may allow black fungus to develop.

In the past, only occasionally did one or two plants host aphids in mid-summer. These pests then were easily dispatched by the hand-squish method. But this year, with yet another very sunny, dry season in the West, I encountered several colonies on a handful of dahlias. That called for more drastic measures. A sharp spray with the garden hose yielded some positive results but did not eliminate all. So stronger methods were needed. At first, in looking at my chemical supply cabinet, I saw a handful of pesticides that no longer are in the market - Diazinon and Malathion (organoposphates) were pulled off shelves due to their potential carcinogenic effect on humans. When systemics were introduced, I viewed these as the perfect environmental solution to combating insects, as they could be applied at the base of a plant, rather than by broadcast spraying the garden. At first I bought Ortho Isotox, then on the recommendation of a veteran dahlia raiser (now deceased) also the more powerfully toxic powder Isotox 2.

Since then I learned to avoid broad spectrum systemic insecticides altogether. Yes, they poison a plant and so can kill pests, but they are indiscriminate in that beneficial insects like bees, wasps, lacewings, and yes! – earwigs – also succumb to that potion. Not to mention how all such insecticides affect the health of the underground flora and fauna kingdoms so necessary for a naturally-balanced soil. Both forms of Isotox are highly toxic and deemed carcinogenic as well, so they no longer are available.*

My supply cabinet also will be emptied of these harmful potions and replaced with Spectracide and other pyrethroid sprays - more natural pesticides, as their active ingredient is derived from chrysanthemums. I did have a can of Ortho RosePride spray (also a pyrethroid) and that did the trick this time. Like Talstar P, preferred by some dahlia experts, it has bifenthrin as the active ingredient. Although using garden aerosols often harms the foliage, only a few signs of damage were apparent - and the aphids were no more.

Yes, there are still other aphid controls and home remedies for insects in the garden. For one, aphids get preyed on by ladybugs - or rather, ladybug larvae. These fierce-looking alligator-like marauders will munch on aphids, but the reason few larvae are offered in stores is simple - they are tiny and their adult-stage bugs can more easily be harvested. So as soon as ladybugs are released, they may simply fly away. A better result are found with adult green lacewing flies, known as predators of soft-bodied insects like aphids and mites. They’ll remain in the garden so long as there is easy prey to pursue.

Some gardeners swear by less toxic insecticidal soaps, often made with fatty acids or oils and dishwashing soap. The oils allow the mixture to stick to the plant and its insect tormentors. Then there is neem oil, praised for its insecticidal and fungicidal properties. Some of this exceeds its promises, but a combination of neem and soap appears to be more effective for insect control. Note: Such formulations are effective only if sprayed directly onto the aphids. Once dry, insecticidal soaps lose their potency. Several tested commercial products offer these more environmentally conscious approaches, if squeezing aphids between thumb and forefinger is tactilely offensive.

*There are disposal directions on the pesticide’s label, provided you still can read that. If your community has a hazardous waste disposal program, bring any of these banned containers there for safe handling. Otherwise, place them in a plastic bag and put them in the household garbage trash can.

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Martin Kral and Dianne Reitan, co-authors of the Dahlia Talk,

are shown here at the 2023 ADS National Show in Portland, Oregon.