7/2/2013 - By Dr. Travis Shaddox

As winter turns to spring, we find ourselves busier than ever trying to keep up with plant demands.  Fertilizers, pre-emergent herbicides, and fungicides are being applied so quickly you may now be looking to hire additional employees just to keep up.  Obviously, this is a great problem to have!  But before our agronomic vision becomes singularly focused on products and people, it is important to remember the big three variables that can be your greatest agronomic ally or your worst enemy. 

Water, light, and temperature dominate all plant-related variables in terms of plant response.  Your plant will eventually wiltif it does not have optimum W.L.T.  Sure, we can manipulate nature somewhat by using products such as wetting agents, sprayable paints/pigments, or other similar products.  However, if water, light, and temperature are not in sufficient ranges, you will be fighting a difficult battle. 

Water

Water may be the single most important factor influencing plant health.  It is literally the blood of the plant in which nutrients are transferred from leaves to roots and vice versa.  Various drought studies have shown bermudagrass may begin to show drought stress within 5 days of no water and may reach its permanent wilting point within 10 days (Figure 1).

Figure 1. Days to Wilt of Tifdwarf bermudagrass as Influenced by 85:15 sand/amendment

Soil can also influence the plant’s ability to utilize water.  A study conducted in 2003 at the University of Florida evaluated the influence of various root zone materials on the water use efficiency of bermudagrass.  Investigators found when they mixed the existing rooting zone (sand) with porous materials such as humate or clay, bermudagrass was able to more efficiently utilize applied water. 

Not applying sufficient water is obviously an issue.  However, applying too much water is also a common problem.  Ideally, the soil’s porous space should be filled with 50% water and 50% air.  Generally, overwatering becomes an issue only in poorly drained soils.  Under saturated conditions, plant production can decline because the roots of all but a few specialized plants (cypress, rice, etc.) require aerated soils for respiration.  Furthermore, nutrients can be reduced and lost to the air via transformation processes such as denitrification.  That is a fancy way of saying, “You just lost money because the nitrogen you applied is now floating in the air rather than feeding your plants.” 

Not only does water quantity influence plant health, but water quality does as well.  Each year more and more turf and landscape managers are being asked to replace potable water with effluent water.  Effluent water (purified waste water) can contain high levels of salts which, in turn, can have a detrimental effect on soil permeability and plant development.  Nearly any soil testing lab can provide you with an accurate salt content of your irrigation water.  Once you have your water analyzed, you may refer to Table 1 to determine if salts may be an issue at your location.

Light

All but a very few specialized organisms depend upon the sun for survival.  Thus, photosynthesis is the most important process on earth.  Each plant has a specific requirement for light which may vary from only a small amount of shaded light to as much as 12 hours of direct sunlight per day. 

One of the more handy tools is the iPhone app “sunseeker” from ozpda.com.  It is a photography app that is perfect for determining the length of sunlight a particular area receives.  All you need to do is stand in the location you are interested in and hold the app in line with the current sun path (Figure 2.)  The app tracks the path of the sun and gives you the time of sunrise and sunset.  In Figure 2, you will notice the sun’s current path (the yellow line) is block by the trees at 8:00 am but is clear of the trees around 8:30.  The red line in the top left corner is the sun’s path during the summer solstice and the blue line is the sun’s path on the winter solstice.  Using an app like this allows you to quickly and objectively explain to a homeowner or customer that the location may have growth issues due to a lack of sunlight. 

Figure 2. Screenshot of Sunseeker

Temperature

Temperature can be easily overlooked as a major factor that can influence plant growth.  Often times, this is due to the delayed plant response to temperature changes.  Several years ago I was involved with a customer who had walked his properties one spring day and noticed dozens of acres of turf damage.  Through numerous discussions, we could not definitively determine any product or operator issues that could have caused the damaged.  Additionally, damage was observed on properties our customer managed as well as adjacent property managed by another company.  When we pulled the temperature data, the problem was clear.  Seven days before the observed damage, a late season frost hit the area, and because it had occurred a week prior to the observed damage, nobody thought about temperature being an issue. 

Warm temperatures can also throw your plants out of their normal growth patterns.  Augusta Georgia is well known for hosting the world’s most prestigious golf tournament, the Master’s.  If you have ever viewed the tournament on television or in person, you probably noticed the flowing white and pink azaleas in the background of nearly every golf hole.  Unfortunately for some, this year those white and pink azaleas had already come and gone before the tournament started.  This was due the unusually high temperatures we experienced in the southern U.S. this winter and spring. 

While fertility and pest management are essential for optimal plant development, let’s not forget to keep an eye on the larger picture of W.L.T.  Maintaining optimal levels of W.L.T. for your plant will make your job a lot easier and, in the end, produce a more satisfied customer.