I got a call the other day from a concerned homeowner. Seems he’s got brown spots in his lawn and he claims his pest control company doesn’t know how to handle them. “I told them,” he yells through the phone, “you gotta apply insecticides. That always took care of our lawn up north. It happens every year about this time and that’s what I always did. But, no, they tell me that’s not the problem and they can’t treat it with anything. Doc, do ya think I should fire them?”

So, which of the following responses did I give?

1. “Sir, if you know so much, why don’t you buy the pest control company?”

2. “Sir, did you see any insects? Have you done a float test? Have you checked your irrigation in those spots? What do your roots look like in the affected areas? Is the area shaded?”

3. “Well then, why don’t you move back up north and bother someone there?”

4. “Tell them to hit it with everything – insecticides, fungicides, even some herbicides for good measure. And don’t forget the fertilizer – lots of it!”

Fact is, not all brown spots in lawns are chinch bugs or brown patch. Often times, the cause of the stress might not be due to a biological organism at all and pesticides will not solve the problem. Often, environmental issues are causing the problem and these must be addressed to eliminate the problem. Environmental stresses can include shade, drought, over-watering, nutrient deficiency, scalping, traffic, salinity, animal wastes, soil compaction, cold temperatures, and other non-biological effects.

Management of environmental stresses falls into two primary categories:

1) selection of the most stress-tolerant species or

cultivar for a particular area, and

2) proper cultural and management practices to alleviate the effects of stress and maintain an adequate carbohydrate supply.

PLANT SELECTION

We’ve all heard the “right plant, right place” mantra, but when it comes to lawns, how often can you persuade your customers to replace what they have? Replacing a lawn is right up there with undergoing major surgery for many people, even if the species or cultivar they have is not performing well. Table 1 provides environmental and biotic tolerances and management information on some of the lawn grasses currently used in Florida.

PRACTICES

TO ALLEVIATE

ENVIRONMENTAL STRESSES

Sometimes proper management will allow a species or cultivar to grow in an adverse environment – at least for a while. Or perhaps conditions are not optimal, but can still support grass growth. With the expense associated with replacing a lawn, it may be possible to encourage a suitable plant response in some adverse situations; however, it is important to make your customers understand that the lawn may not look optimal and may be more subject to biotic problems of insect, disease or weed pressure due to the environment.

Management strategies for environmental stresses include:

• Growing a deep root system

• Appropriate fertilization practices

• Appropriate mowing practices

• Reduction of additional stresses

GROWING A DEEP ROOT SYSTEM

Roots are truly the backbone of a turfgrass plant and a lawn that has amassed deeper roots will often be able to survive a stress that another lawn might not. Two factors to promote deeper roots are:

• Mowing at the proper height – mowing too low or repeated scalping will force the grass to put its energy into re-growing the shoot system instead of the root system and roots will remain short. This makes the grass weak.

• Irrigating correctly – irrigating to provide water slightly deeper than the roots will encourage roots to grow down to the water. On the other hand, applying minimal amounts of water that only wet the top of the soil will encourage roots to remain in that area instead of growing down. This again leaves the grass in a weakened state.

A deep root system will not only help the grass survive droughts better, it will make it better able to tolerate any other stresses as well. Strong roots, strong grass!

APPROPRIATE FERTILIZATION

PRACTICES AND PHOTOSYNTHESIS 101

Grass uses nutrients to grow – we all know that if we apply nitrogen (N) at the appropriate rates and right times, the grass will green up and produce more shoot tissue. Plants also use nutrients not found in fertilizer through the process of photosynthesis. In this process, plants intercept and convert sunlight into energy for growth or storage. In combination with nutrient fertilization, photosynthesis provides the plant with the building blocks for new root and shoot growth. It also supplies the plant with carbohydrates, which are stored for use at a later time. An ample supply of carbohydrate reserves helps the turfgrass plant to green up in the spring, to recover from stresses, and to ensure that continued growth and health can be maintained, especially when the grass is subjected to any kind of stress.

What happens when carbohydrates get depleted? Same as what happens when we get tired and run-down and keep pushing ourselves – we’re more apt to get sick, hurt or depressed. One of the ways we can keep grass healthy is through appropriate fertilization to keep carbohydrate levels high. When we apply too much nitrogen fertilizer, the grass uses stored carbohydrates to support growth flushes. Excessive growth weakens the grass and leaves it susceptible to other stresses, both biotic and environmental. When we don’t apply any or too little nitrogen, photosynthesis is reduced and the plant again does not have enough carbohydrates stored. That’s one reason why we promote “appropriate fertilization levels” to ensure turf health.

It is important to understand what the response of turf under a specific stress will be to nitrogen. Stress from wear injury is a good example of where it is often beneficial to apply a higher level of annual nitrogen to keep the grass growing and recovering from the injury it receives. Other stresses, however, should be treated with less nitrogen. Grass growing in shade is an example of this – it will do better at lower annual N rates.

What about other nutrients? Potassium (K) is an element that seems to have some effect on stress tolerance of turf. Although turf response to an application of K may not be readily visible, K can provide some benefits within the plant that make it stronger. My research on traffic and wear tolerance has shown that K can reduce the extent of wear injury on heavier soils, with little difference found on sandy soils. Under conditions of high traffic, you might try K at rates equal to N. Many turfgrass managers have observed less winterkill and better spring green-up with higher K rates, particularly when applied in the fall. If you are not currently doing so, apply 1 lb of K with your last fall fertilization, especially if you are in the northern or central part of the state. Think of K as a general multi-vitamin for turf – it may not save your life, but it may keep you a little healthier.

APPROPRIATE MOWING PRACTICES

It is important to mow the various grasses at the highest recommended levels for the species or cultivar – mowing lower than this will again cause them to put all their energy into re-growth of the shoot system at the expense of the root system. Scalping is a great way to stress the turf and can not only cause carbohydrate depletion but can also kill the majority of the growing points on the stolons of St. Augustinegrass. You may not be able to control the mowing practices on the properties you maintain, but it is important to pass this information on to the homeowners in the hopes that they will adopt better practices.

REDUCE ADDITIONAL STRESSES

Stresses on grass tend to have multiplicative rather than additive effects. For example, under wear stress, any other problems (insect, drought, scalping, etc.) will cause a far worse response than any of those stresses separately. Trying to reduce other problems may give the turf a fighting edge.

REMEMBER THAT PESTICIDES WON’T HELP ENVIRONMENTAL STRESSES ...

… but pest problems are often caused by primary environmental problems. Attempts to eradicate the pest with a pesticide will not solve the underlying problem. Look for the obvious environmental problems, such as shade, faulty irrigation, compacted soils, bad mowing, etc. These need to be addressed and then any corrective pesticides applied if pests have become a secondary problem. This is one way we can grow healthier lawns, keep our customers happy, have

fewer call-backs, and hopefully apply fewer pesticides.