Pendulum Pre-emergent caused plant die off

Question: I am the president of a small 25 unit HOA in Loveland. Last March our landscape maintenance contractor applied the pre-emergent herbicide Pendulum to our stone borders and gardens, but not the lawn. The application turned everything, plants, rock, statuary, bird baths, etc bright yellow. Within about a week many plants were obviously starting to die at all 25 units. The plants affected included ajuga, miniature roses, hydrangea, spiral grass, and virtually all of the ground cover type plants. The landscape contractor said not to worry as all the plants will come back in a few weeks and the yellow will quickly fade with some rain. The ajuga, miniature roses, hydrangea, daisies and many other garden plants and most of the ground cover type plants actually died. Some ornamental grasses, lilies, bleeding hearts, burning bush and a few others either weren’t affected or recovered. The landscape contractor has continued to insist that it wasn’t the Pendulum product but something else that caused the die off. Any insight you can give me on this situation and the effects of the Prelude product, especially if applied incorrectly would be appreciated. Roger Ulane, Country Lake Villa HOA President

responder: Alison O'Connor, PhD  Replied July 15, 2024, 6:40 PM EDT
response: Hi Roger,  I agree with your landscape contractor that these plants were not affected by the Pendulum (pendimethalin). This is a preemergence product and will only affect germinating seedling plants - not those that are established.  A couple questions:  1. Are these photos recent? 2. Did anyone else do weed control in the landscape beds or has your contractor sprayed anything else? (Also consider a "helpful" neighbor) 3. Do you have photos following the March application of the yellowing?  Pendimethalin is primarily used a grassy preemergence control product, for crabgrass and other annual grasses. It has limited effectiveness on broadleaf annuals. But it would not harm established perennials and woody plants.   The photos you sent look like a non-selective herbicide was applied in the landscape beds.

responder: The Question Asker Replied July 17, 2024, 2:45 PM EDT
response: Alison O'Connor, PhD,   The photos were taken yesterday.  No one else applied any type of product to the affected areas.  The gardens and rock borders with plants were affected at all 25 units.  The attached pictures were taken today showing the yellow sludge that is still present approximately four months after application. The rose in CLV 1 was approximately 24” tall last year with blooms.  The plant in CLV 2 was replanted last week.  After the application it looked as if someone had applied yellow paint with a spray gun.   We appreciate your help.   Roger Ulane, President Country Lake Villa HOA <personal data hidden>       From: ask=<personal data hidden> <ask=<personal data hidden>> On Behalf Of Ask ExtensionSent: Monday, July 15, 2024 4:41 PMTo: Roger Ulane <<personal data hidden>>Subject: Re: Pendulum Pre-emergent caused plant die off (#0147281)

responder: Alison O'Connor, PhD  Replied July 17, 2024, 6:17 PM EDT
response: Hi Roger,  Is iron being used with any of your lawn fertilizers?

responder: The Question Asker Replied July 18, 2024, 9:49 AM EDT
response: No, I don’t believe so.   Could the Pendulum have been mixed in correctly? On Jul 17, 2024, at 4:18 PM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: Alison O'Connor, PhD  Replied July 18, 2024, 4:25 PM EDT
response: Hi Roger,  Pendulum can have a yellow color - as do all the dinitroanilines - but no, it's not from being mixed incorrectly.    It will fade in UV light and be much less noticeable by the end of the summer. If this is a concern, then you may have to consider other preemergence options (or not use anything) for weed control.   You could rake the rock to flip the rocks over :)

responder: The Question Asker Replied July 23, 2024, 12:06 PM EDT
response: Thank you !Sent from my iPhone On Jul 18, 2024, at 2:25 PM, Ask Extension <<personal data hidden>> wrote:   ﻿