Monday, May 18, 2015

Twisty, Narrowed, Thickened Leaves and Other Weedkiller Damage

New growth on tomato made weird by persistent herbicide in manure.
Cabbage growth stunted and warped by persistent herbicide in manure.
There seems to be a lot of weedkiller damage in gardens this year. I've seen twisty, narrowed leaves on rose bushes (from two different yards) that were probably exposed to 2,4-D before the plants even leafed-out in spring; I've seen shortened, odd growth on hydrangeas (same cause); and I've seen vegetable plants whose growth has been stunted and made odd by a group of herbicides that persist in hay, grass clippings, and manures.

Gardeners who are "going organic" probably don't need to worry too much about accidental drift of weedkillers used for lawn-weeds damaging their ornamental plants, because they aren't going to be using weedkillers in their yards. However, the problem with contaminated manures that might be used as soil amendments and with grass clippings or hay that might be used for mulch is another story.
Twisty new growth on tomato caused by persistent herbicide.
Twisty new growth on tomato caused by persistent herbicide.

In this time of persistent herbicides, that idea is no longer 100% true, and it really is up to the gardener to be vigilant and to ask for an "herbicide history" of any amendment that is to be used in the garden.

The tomato and cabbage plants in the top two photos were brought to the office for an evaluation of the stunting and odd growth. The damage is classic for pyridine herbicides. The gardener who brought in the plants had purchased a soil mix (that included composted manure) from a local source for her raised-bed garden.

The third and fourth photos are of tomato plants at a local community garden. The plants had been "bumped up" into pots with a potting mix that included rabbit manure. Anyone who has read this blog for very long knows that I have pet bunnies, and that my bunnies contribute some great manure and timothy-hay bedding to my compost pile, so this was an alarming discovery for me.

Some of the tomato plants were affected more severely than others, with Beefsteak showing the least damage and Banana-legs showing the most.
The good news for this community garden is that the plants were not yet planted in the ground when I went out to see the garden for an unrelated problem (blueberries with yellowing leaves), so the garden soil was uncontaminated.

For fuller information about the problem with persistent herbicides in compost, manure, and hay, see NCSU's publication "Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings."

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