Irrigation or rain activates the herbicide so it binds to the soil, and while watering-in an application as soon as possible is best, it should be fine to wait for rainfall later this week if you can't irrigate manually. Do not make additional applications unless the product label specifically instructs the user to do so.

We discourage the use of weed-and-feed products for a variety of reasons, including the difficulty in adjusting application rates or timing based on what a specific lawn needs. Fertilizer cannot be over-applied without violating the Maryland Lawn Fertilizer law, plus it would be adding more nutrients than the turf can make use of anyway.

The timing of Crabgrass germination depends on soil temperatures, and we are just about there for many areas of the state given our recent warm weather. The linked page provides more information and includes a resource where you can look up average local soil temperatures for the purposes of estimating the ideal timing of a pre-emergent herbicide, since they work by preventing germination as long as they are applied before that event.

Long-term, avoiding conditions like mowing too low, not annually overseeding the lawn with tall fescue, and other routine lawn care management tips will help the lawn stay vigorous and dense enough to out-compete most weeds (including Crabgrass) by itself.

Miri

Hi

We got a thunderstom early Monday and more rain in the morning.  

The weater is hard to predict.  If you put down the dwon in late March no mater what the soil temp may be, will it prevent the weeds includng crab grass?

Will Halts stop chickweed ?

Pre-emergent herbicides work by forming a chemical barrier to germination on the soil surface, binding to the soil once it is watered-in (rain or irrigation), as that activates the chemistry of the herbicide. As long as the active ingredients in the herbicide don't volatilize (evaporate) or disperse in some other way before a rain event can activate them, presumably you can make an application ahead of time and wait for rain to make it active, as long as it's been put down prior to the expected start of a weed's germination window. A second application of the same herbicide might be needed about 6-8 weeks after the first, so if one is missed, a later application might still provide some benefit for any late-germinating weed seeds. Any questions about the more precise range of timing, though, like how far ahead of rain the product can be applied, will need to be determined from the information on the product label. (Or, if it doesn't specify, by contacting the product manufacturer to ask.)

We can't say whether it will affect chickweed because this information is on the product label, which we do not have. (While we can look up versions of it online, that won't tell us which exact version of its label you have in hand, or which formulation of that brand you are using. Manufacturers occasionally revise their product labels, or reformulate the product itself.) Since a pesticide label is the law with regard to legal usage, we must defer to whatever the label states in terms of what weeds is it targeting, plus where and when it can be applied. We find it unlikely that a broad-spectrum broadleaf weed killer would not impact chickweed, since it's such a common lawn and garden weed. Since annual chickweed dies in spring, though, an application of pre-emergent herbicide for this weed must be made sometime in autumn (or even late summer), since that is when the seeds will be germinating for this and other winter annual weeds; a spring application of pre-emergent won't have any impact on chickweed, though a post-emergent (a chemical affecting already-growing weeds) probably will.

Miri

Winter annual weeds germinate in late summer or autumn, so any pre-emergent needs to be applied prior to this period of germination. If a product label doesn't provide instructions for making applications for this category of weeds, then it might not be the right herbicide to use for that situation, since it's a legal requirement that pesticides (which includes herbicides) be used in accordance with their label directions. Since we don't have the exact copy of the pesticide you're using (its label is on the package), you can check if it outlines how to apply it for those particular weeds (Poa annua, etc.).

Dandelion can be favored by mowing lawns too short and not having dense growth, though occasionally some individual plants might still colonize a lawn and reach flowering age. They can be spot-treated with a systemic herbicide once you notice them, ideally before bloom and seed formation, of course. Our dandelion page does not list any particular recommendations for ingredients to use as a pre-emergent. If only a few appear in an expanse of lawn, it will use less herbicide overall to spot-treat those that do manage to survive competition with the lawn, compared to broadcasting pre-emergent over the entire lawn. This happens to be a good illustration of how a lush lawn (yours, as pictured) can out-compete most weeds on its own (which may be why the neighbors have more of them, if their lawns are not regularly overseeded, aerated, or managed in a similar way).

We do not recommend using a pre-emergent over an entire lawn when a particular weed only appears scattered in a few places, but if you try one, you'd have to look for a formulation that includes dandelion and follow its directions for application timing. Fortunately, dandelion seeds are not long-lived in the sense that the same seed bank (accumulated fallen seed over the years) will not support multiple years of germination.

Miri

Hello Stan,

The mention about dandelions not being long-lived referred to seeds in the seed bank, which means the dormant seeds lying in the soil surface layers that can germinate when given the chance (the right weather conditions, plus being at the right depth in the soil). Seeds have a "shelf life" and will only live for so long in their dormant state, so not having a long life in the seed bank means that if they can be prevented from germinating (by not disturbing the soil, mainly) for a few years, they will expire. Yes, any time seed heads blow around, more seed is being added to the seed bank, and yes, the plants themselves (once up and growing) are perennial, so can live for several years if not treated or physically removed.

The product label is not the excerpted information shared on the brand's web catalog (or on any other supplier's web page for that product)...it is the actual label printed on the product container (bottle, box, or in this case, bag). It is a legal document, and federal law requires that it be followed as written, so whatever dosage and application information is on that bag's label is what needs to be followed, assuming it complies with Maryland law as well with regards to any fertilizer component. Sometimes brands have the label available as a viewable/downloadable PDF file -- it's typically a multi-page document -- but the label on the physical bag takes priority since it's the version of the label that applies to that specific batch of pesticide, in case the manufacturer made alterations to its chemical concentration, chemical makeup, or instructions for use.

One of the main reasons we do not recommend using weed-and-feed overall is because lawn fertilization should be performed based on the results of a laboratory soil test, which analyzes the nutrient levels already present (and the acidity, or pH, since that influences nutrient absorption by the roots) to look for any deficiencies. Since the ideal timing of a weed preventer might not align well with the timing of fertilizer applications, or even the nutrients needed (since a combo product doesn't let you customize what you're applying based on what your lawn actually needs), that can be a hindrance of applying both together.

Miri