Can I use herbicides in flood conditions without harming good plants?

Question

In Arizona, USA, it is monsoon season, meaning that our dry, arid, and rainless state suddenly gets a lot of rain over the period of about two months. This sort of flooding is perfect for spreading seeds and germinating weeds.

My yard has horrible drainage, so when it rains, the yard becomes a flood pool two inches deep, including around our fruit trees and non-weed bushes. Optimally, the solution is to hire a landscaper to fix this drainage issue (it isn't good for the house, either), but right now my finances cannot afford it.

Problem: The monsoon is sprouting all the weeds.

Question: What can I do?

I feel like my only solution is to futile hoe the entire yard every week. I am worried if I put down herbicide spray or pellets, the next rain will make the yard a pool again, diluting the poisons and spreading them to my non-weed plants and trees.

Another way of approaching the question might be "Herbicides are rainproof, but are they flood proof?"

Answer 1

I'm assuming from your reference to hoeing that this is not lawn, so you can use a broad spectrum weed and grass herbicide. The best one in your situation would be Roundup (glyphosate) a systematic herbicide.

Roundup is absorbed by the plant it is sprayed on in less than two hours (advertised 30 minutes), so flooding will not decrease the effectiveness on treated plants. It also becomes deactivated within three days of spraying (references 1, 2, 3), so if you wait for a break in your monsooning, you will not have an issue with damage to your ornamentals.

However, there will be partially broken down roundup that will mix into your flood water, and soak into the soil, and may linger for quite a while, given your long dry season and less than ideal soil. You shouldn't use roundup on waterways, which sounds like it fits with you (re. drainage). After the initial kill, you could consider a pre-emergent herbicide, which will prevent weeds from germinating, and won't harm your ornamentals.

Update in response to comment:

My concern with the pre-emergent was that I'd lay it down. And then the next time it rained and flooded the yard a few inches, the places I treated would become diluted, reducing its effectiveness severely. Will this be an issue?

If your yard is sloped, this may be an issue. If it is flat for the most part, the pre-em will at least help. You can just stick to post-em control if you feel like it would work better for the money spent.

Answer 2

You can take a line trimmer and chop the top off the seedlings, pretty easily. Burns calories and it is the least expensive thing you can do. You can even take a rake and rake the little seedlings spreading them out in the sun. I know Arizona a little bit and it is mighty tough for anything to become invasive.

Your instincts are good...don't use herbicides. Your water table down there is in big trouble and a little herbicide is a big deal for water quality.

Weeds are nothing more than a plant out of place. They do happen to be less demanding and can survive better than...ornamentals. If you can stay vigilant, go out once or twice a week to chop the tops off or using a 'hula hoe' disrupt the roots, that is all it will take to keep them in check.

The other thing I would do would be to find a facility that composts human sludge and sawdust. They should be testing 4 - 5 X and be able to give you a printout on test results. The final product should smell wonderful, like the earth. Be dark taupe in color, fine textured, no sticks, no rocks...this is all I use for my lawns and plant beds. This will turn your sandy soil into water holding, nutrient holding, organism rich soil. All you have to do is dump it on your soil and the organisms see a virtual neon sign saying "Best grub in AZ! For Free!"...they will come, eat this decomposed organic compost and take it back into your soil profile, mixing it for you.

Not only will this improve your AZ soils, hold moisture longer, hold nutrients longer, add nutrients and soil beneficial organisms...but it is the best stuff to smother seeds you don't want germinating. 2" on top of these seedlings will turn them into compost AND you'll be vastly improving your soil for the plants you want to prosper. Can't use it for vegetable gardening as it IS a little high in heavy metals. Of course 3/4 of our world uses human poo for fertilizer (rice paddies, etc.)

Doesn't matter what kind of soil one has, the ONLY way to improve any soil is by adding decomposed organic matter. That is a fact. The worst soil one can imagine can become totally productive with just the addition of decomposed organic matter. Maybe adding fertilizer...but fertilizer won't be used well by plants without the pH stabilizing, micro and macro-organisms that are there only because there is readily available food of decomposed organic matter.

Killing two birds with one stone: Smother your weeds, weed seed while feeding your soil. Let me know if you are able to find a supplier! My kids live down there and I could pass the info along.

Where in AZ are you? Please send pictures, we could help you with drainage issues as well which you should address soon. Are you buying this home? Send a base plan of your home and property with property lines, utilities, outbuildings, neighbors, fences, drive way, walkways, vehicle access, North orientation, plants that exist and please include at least 3 - 6 elevations. This means the height at 6 different spots in relation to...the elevation of your home. You can get a transit, laser to do this. Ask a friend in construction to do this for you in exchange for washing their car, making dinner and washing dishes.

Look through your mortgage documents for an 'As-Built'...most of this should already be accomplished. Find out if you're foundation is 'slab', 'pier', foundation with crawl space or basement. What did they do for drainage when they built your home? Foundation drainage, asphalt emulsion, anything you can find about what you own and how it was constructed. Take pictures of your basement, foundation, your property with high and low points. Use graph paper, 1/4" to one foot or whatever scale makes sense to you. Take a picture of your drawing and send it. Let us see what we can do with that information.