Roots, Shoots, Fruits & Flowers: Suspected Potassium Deficiency, Herbicide Damage, and Mystery Gall

A closeup of the leaves of a fruit tree.

Granny Smith apple tree has potential potassium deficiency

“This is a newly planted Granny Smith apple. What is wrong?” asks Susan.

Based only on this photo, AHA suspects the early onset of a potassium deficiency. Mr. Eric Hanson, a horticulturist with Michigan State University, described the symptoms of potassium deficiency, “Deficiencies result initially in a yellowing of tissue along leaf margins. That tissue later turns a bronze color and may eventually die, producing a scorched zone along the edges of leaves as the deficiency progresses. Scorched areas do not extend between the veins of leaves. Because K is mobile, symptoms appear first on older leaves but may affect young leaves in severe cases. Fruits accumulate large amounts of K, so leaf symptoms are more likely and severe as fruit approaches maturity during heavy crop years.”

Because this young tree has no fruit, the suspected lack of potassium seems to be especially visible. Dr. Raj Singh, plant disease specialist with the LSU AgCenter, also examined Susan’s picture and responded, “It could be a nutrient deficiency. Is it watered regularly?”

Watering is an easy fix for this apple tree. However, a soil test is needed to confirm the lack of potassium or another nutrient. The good news is that the AgCenter’s Soil Lab is now back in operation. The next step is to create a safe means of handing out the AgCenter’s soil test kits to gardeners who wants to keep their plants happy.

A close up of a tomato plant with herbicide damage.

Tomato plants have yellowing leaves

Gerald emailed, “I have 6 - BHN 444 tomato plants, all are showing this yellowing of the leaves, some more, then others. They are in fresh compost ‘first year’ raised bed. Is this something I need to worry about? Or not so much?”

Gerald’s tomato plant has the classic symptoms of herbicide damage. Sometimes, uncomposted animal manure will have herbicide residues and cause damage through the roots of the vegetable plant. Gerald later emailed that he bought his compost in bulk from a nursery. However, other vegetable plants growing in this compost were unaffected. The most likely explanation is that some of the bulk compost was contaminated and some not. The batch mixing failed to spread the contaminated manure throughout the batch so some of Gerald’s plant avoided damage.

A mystery gall on a muscadine vine. Photo: unknown

Muscadine stem gall

Silas Cecil, an AgCenter Extension Agent in LaSalle Parish, sent this message, “[I] had these attachments sent to me today. [I] don’t know what they are attached to (I tried to find out). [It] came through Facebook Messenger. Take a quick look to see if you can provide more insight!” Silas also mentioned that this image occurred in a wooded setting, so the infected plant shown is probably a muscadine vine.

AHA searched various extension websites to look for “muscadine stem gall” and for “grape stem gall”, and the gall images on those websites had zero resemblance to the image sent with Silas’ email. AHA consulted the AgCenter’s plant doctor, and he replied, “I am not sure [of] the cause of [the gall].”

This gall resembles the leaf galls of camellias and the stem galls of sweetleaf, a small forest tree. If readers have seen this mystery gall on muscadine or grape vines, they are encouraged to contact AHA.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

4/22/2020 6:36:22 PM
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