RESEARCHING MAINTENANCE

Granular vs. liquid

What is the difference between granular and liquid broadleaf herbicides? — via the Internet

Liquid products can be applied with thorough leaf-surface coverage, which maximizes the amount of herbicide that can enter the target weeds. Granules, by contrast, can only transfer the herbicide into the foliage of the target weeds through the point of physical contact, which can be quite small or even non-existent, if the granule simply falls to the soil surface after bouncing off a leaf.

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The practical upshot of this is that granules must be applied when moisture is present on leaf surfaces, such as on a dewey morning or after an irrigation. This causes them to stick to leaf surfaces, increasing the amount of herbicide acting on the weeds. Even then, the degree of control may not match that of liquid spray applications. Plus, you cannot apply anytime you feel like it … the turf must be moist. Finally, spot treatments are not very practical with granular products, so liquids offer that advantage as well.

Granules do offer some advantages, however. First, they can be applied with a broadcast spreader for efficient application over a large area (granulars are generally easier to handle and load, too). Second, they are not as susceptible to drift as sprays.

Granular products are often formulated with fertilizers as “weed and feed” products, which is convenient. However, liquid herbicides can be tank-mixed with fertilizers as well.

Dealing with clay

What's the best way to deal with adobe clay soils? — California

Heavy clay soils are the bane of landscape managers almost everywhere. Actually, clays can support good plant growth, particularly once the plants become well established. Clays retain water and nutrients better than other soils. However, you must manage water carefully and avoid selecting plants that are sensitive to damp conditions. In addition, compaction, to which clays are especially prone, must be mitigated.

Prior to installing turf or ornamentals, you may want to amend heavy clays. Organic matter is a good choice. Heavy amounts will temporarily help keep the soil physically loose and porous, which is a great aid in getting roots established. Many installers till organic matter into soil before turf seeding to aid establishment.

In truth, the long-term benefit of a single organic-matter amendment is debatable and probably minimal. Several studies have shown that plants do not establish any quicker when the hole is backfilled with organic-amended soil. What definitely does aid them is the loosened soil. This may partly be why so many people swear by organic planting amendments — in the process of mixing in the organic matter, they are giving the plants precisely what they need: loosened the soil.

Sand might seem a logical amendment for clay, but only if you apply proportionately large amounts (perhaps in excess of 50 percent by volume). That is not often practical, and so it is seldom done. Using inadequate amounts of sand can actually worsen the soil.

Other tips that help with clay soils:

  • Never till when clay soil is wet. This can be a frustrating exercise when you need to plant and the wet weather won't let up, but you will pay dearly if you till before the soil dries down. The resulting clods will be impossible to break up.

  • Similarly, avoid traffic of any sort on wet clays. Traffic can compact most wet soils, but clay is especially susceptible.

  • Smaller, more frequent doses of irrigation water may be necessary to match the lower infiltration rates of clay soils. This is especially critical on slopes. Drip irrigation can be especially helpful in such cases.

  • Monitor soil moisture conditions carefully and withhold water if clay soils are excessively moist. This will reduce soil pathogens that tend to attack roots in wet conditions.

  • When you install top soil or “black dirt” on top of a clay site, be aware that plants growing in the top soil may have little success sending roots into the underlying clay, especially if it is highly compacted, which often is the case with new installations.

Eric Liskey has a bachelor's degree in ornamental horticulture and a master's degree in botany. He has been licensed for pesticide advising and applications in California and Missouri, and has more than 10 years combined professional experience in landscape installation and maintenance, nursery retailing, pest management and botany.

If you have a question about landscape or turf management, write to “Researching Maintenance,” Grounds Maintenance, P.O. Box 12901, Overland Park, KS 66282-2901, or send you question by e-mail to eliskey@primediabusiness.com.

Questions are selected on the basis of current general interest. Unfortunately, we are unable to guarantee a response to individual letters.

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