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Saturday, April 28, 2018

Leaf Yellowing of Pomegranate Could Be Weed Killer

Q. Eleven of my 50 young pomegranates have leaves yellowing and dropping off. I water this area once a week by flooding. I sprayed a weed killer, 2,4-D, near the pomegranates but I protected each one with plastic to avoid damaging the trees. Where did I go wrong here? If the weed killer is the problem, is there any way to save them?
It looks like the pomegranates were planted in a depression. The more I look at these pictures the more I'm concerned that it the roots may be kept too wet. The only way to know for sure is to use the soil moisture meter and measured the soil moisture just before the next irrigation. Generally speaking, pomegranates and most long grasses are not compatible. Another possible option is to plant pomegranates on a raised area of soil rather than a depression.
Even though the soil is cracked on the surface it tells you nothing about how dry it is only a couple of inches below the surface. Many weed killers can travel with water. Make sure no water is added to these plants within 24 hours after we killers are sprayed on the soil.

A. When I first saw your pictures I thought the soil was too wet. But I read your email that they were watered only once a week. Watering once a week in mid spring should pose no problem if the soil is not a heavy clay. If the soil is a heavy clay and remains wet a couple of days, this could cause leaf yellowing and dropping.
            In the picture, I saw grass growing close to the pomegranates. If watering only once each week, I assume the grass is Bermudagrass. Tall fescue should need watering more often than this. Grass growing close to these trees will cause them to grow more slowly. Particularly Bermudagrass. So it’s always a good idea to remove grass at least 3 feet from a fruit tree.
            The leaf yellowing could also come from a lack of nitrogen in the soil. However, if you are fertilizing that grass there is probably plenty of this fertilizer escaping to the pomegranates. Removing grass 3 feet from the tree will reduce competition for any fertilizers applied.
            Now on to the most likely problem; weed killers. It helped that you covered each of the trees with plastic before spraying. It’s even more important if you spray this kind of weed killer when temperatures are cool and there is absolutely no wind. Hot soil surfaces cause dandelion killers like 2,4-D to volatilize (turn into a vapor) and move very easily with the very slightest air movement.
This is 2,4-D damage, dandelion killer, on tomato. If the tomato plant is growing, the growth will become deformed.
            Damage from 2,4-D is easy to identify when the plant is growing and producing new leaves; new leaves are deformed. If the plant is not growing and producing new leaves, leaves turn yellow and drop. The branches that supported them may or may not die as well. All you can do is wait and see what happens.
This is weedkiller damage on grape. The weedkiller is unknown but the damage is unmistakable.
            I am concerned with the plastic. Make sure that the same side of the plastic using contact with the plants and that you don’t accidentally wrap the plant the wrong way.
            I think a better weed killer to use for your purpose might be Roundup. It does not volatilize as easily as 2,4-D. For it to work, the spray must land on green leaves or green limbs. If you prune pomegranates so their lowest foliage is about knee height from the ground, it will be less likely to be damaged.
            Keeping grass 3 feet from the trunk will also help. A small plastic bucket with a hole drilled in the center of the bottom, attached to a spray wand, will help contain the spray and directed toward the weeds.

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