Roots, Shoots, Fruits & Flowers: Purple Leaves, Royal Paulownia, Mistaken Identity and Pre-Emergent Herbicides


Purple leaves indicate phosphorus deficiency. Photo: Austin Urban Gardens

Purple Leaves

A gardener came by the AgCenter office with a sampling of blackberry leaves that looked like these.

During the winter months, leaves of several different plants can turn purple. If you look at your lawn, you may see purple in your turfgrass. Purpling is an indication of the lack of phosphorus. However, this purpling of foliage during the winter is normal because cooler temperatures prevent the movement of phosphorus in plants. If, on the other hand, purple leaves occur during the growing season, then a soil test is needed to see how much phosphorus your plants will need. A soil analysis from the AgCenter will have recommendations for the correct fertilizer rates including phosphorus.


Seed pods and leaves of a royal paulownia tree. Photo: Barry Lee, Pineville.

Royal Paulownia

Barry from Pineville sent an image on behalf of a friend asking to identify a tree and share this picture.

The seed pods and the leaves in this image are from a royal paulownia, a non-native, invasive tree from Asia. Each of the seed pods seems to have hundreds of tiny, wind-borne seeds so this tree can spread quickly if it is not under control. The leaves are large and heart-shaped, and this trait enables easy identification of this tree.


A muscadine vine with "weird buds". Photo: Christy Frederic, Master Gardener.

Mistaken Identity

Christy, a regular contributor to RSFF, sent an image with a strange “growth” and asked, “I found these two weird buds on a mature muscadine vine when pruning yesterday. All the other buds were small…. Any thoughts? “At first AHA thought these “weird buds” may be a gall from an insect or disease so he consulted with Dr. Mary Helen Ferguson who works with small fruits.

Dr. Ferguson shared this comment,” From what I can see, it looks like some buds from another plant may have gotten entangled with a muscadine tendril. You might ask her if there was another plant close by that they could have come from.” Christy then confirmed Dr. Ferguson’s diagnosis, “Well she is right! I just went look at the little tendril and sure enough it was coiled around camellia buds!!! Did NOT see that before! Thanks so much!!!” Apparently, what we have here is a mistaken identity!


A cyclone spreader is a good tool for applying dry granular products like pre-emergent herbicides. Photo: University of Nebraska-Lincoln.

Pre-Emergent Herbicides

Elaine did her due diligence and asked about the correct use of an herbicide, “I’ve found a really good article on pre-emergent herbicides that I wish to send to [my] Garden Club. The only problem is that it was written by someone in Delaware. It states to apply in the middle of March when the forsythia blooms. Well, that would be a lot later than our forsythia. When would be the correct time for us to put out our pre-emergent herbicides? I have attached the article so you can see if it would apply to us.”

First, Elaine made the correct decision to contact the AgCenter about the safe and effective use of a pesticide. She also recognized wisely that advice that works for Delaware may not work in Louisiana.

With any pesticide, an applicator needs to read the label for using a product correctly and safely. The AgCenter applied a product called Preen™, a pre-emergent herbicide, to controlled trial sites and found this product to be effective in preventing weeds while leaving existing plants unharmed. The label for Preen™ discusses when to use this product, “Apply Preen Garden Weed Preventer during the growing season around established plants and transplants. Preen should not be used on flower seeds. It can be used after flowering plants have germinated and are 2 – 3 inches tall.”

So, the answer to Elaine’s question about when to apply would depend on the label. In the case of Preen™, the answer would be any time during growing season of both warm-season weeds and cool-season weeds, which means any time.

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.

“Before you buy or use an insecticide product, first read the label, and strictly follow label recommendations. Mention of trade names or commercial products in this article is for informational purposes only and does not constitute endorsement by Louisiana State University AgCenter.”

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

1/26/2021 10:26:43 PM
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