Saturday, March 17, 2018

Mulch with Wood Chips

 Mulch placed around plants is a good way to conserve soil moisture. Plants that have a layer of mulch over their roots will manage better in a drought situation. Wood chips, when available, make an excellent mulch for other reasons also. 

  • A wood mulch layer can help prevent diseases by keeping fruit like strawberries and tomatoes, from touching the fungal infested ground. The same mulch layer will create a barrier, preventing rot causing fungal spores from splashing up onto low growing citrus fruit. Wood mulches also produce chemical compounds that inhibit the growth of disease causing fungi. Furthermore, a layer of mulch will help to control erosion and reduce weeds. Apply at least 4 inches for good weed control.

When incorporating large quantities of non-composted wood products like sawdust and wood chips into the soil, it’s a good idea to add a little high nitrogen fertilizer to prevent a nitrogen deficiency.  This can happen because bacteria require nitrogen as they break down the wood and will take it from the soil. It is only temporary though, because as the bacteria die, they will release the nitrogen. This is especially important for newly planted annuals like flowers and vegetables. Established trees and shrubs, however, have a large enough root system to obtain nitrogen from deeper depths.

Sunday, February 18, 2018

Black Sooty Mold

What is the black, sticky substance that may be found covering the leaves of many plants?
The black substance on the leaves is called sooty mold.  It is a fungus which resembles soot. This particular fungus, however, is not harmful to the plant but is actually living on a sweet, sugary substance called honeydew.  The honeydew is being secreted by some insect that is infesting the plant. If you see sooty mold on a plant, it means that the plant has an insect infestation – most likely aphids, mealy bugs, soft scale or whitefly. 

As the insect feeds, a clear sugary liquid is secreted by the insect onto the leaf below.  It is on this secretion that the mold grows.  Heavy rains will wash off the sooty mold from the leaves, but the insect problem still needs attention. Often when large trees become heavily infested with certain insects, the honeydew can actually be seen raining down upon the ground.  Again, sooty mold indicates an insect problem; inspect the plant for bugs.  Below is a close up of the sooty mold.

Monday, January 29, 2018

Lawn - the Control of Weeds

Broadleaf weeds appear in the grass.

Controlling weeds in the lawn should begin long before chemical herbicide applications are considered. Cultural measures ought to be employed from the beginning. These include: 
  • Proper irrigation -  weeds often invade lawns that are either over-watered or under-watered. Perhaps the worst possible irrigation schedule, yet common, is daily watering for 5–10 minutes. Light, frequent irrigation creates a shallow-rooted lawn which is more susceptible to weed invasion, as well as being less tolerant to drought.  In dry areas, where irrigation is employed, water should penetrate to a depth of 6 to 8 inches. The best practice is to allow the soil to partially dry out between irrigation. The top 1 to 2 inches  should be fairly dry before watering again. For more information on irrigating lawns, see UH CTAHR publication, “Watering Lawns”, at
  • Proper fertilization – apply suitable amounts of fertilizer on a regular basis; nitrogen is the key nutrient for turf.
  • Proper mowing heights – each turfgrass species has an appropriate mowing height. Mowing some grasses too short can weaken the lawn and predispose it to weed invasion.  A typical guide is to remove no more than one-third of the leaf blade at each mowing. If too much is removed, it will take more time for the grass to recover, giving weeds a chance to invade.
  • Thatch is a layer of organic matter - stems, stolons, roots - that develops between the turfgrass blades and the soil surface. Regular thatch removal will help keep turfgrass healthy and competitive with weeds.  For Hawaii residents, see the UH CTAHR publication “Removing Thatch from your Lawn” for more information on this procedure.
  • Any activities that lead to soil compaction will contribute significantly to turfgrass stress. This in turn, will make it easier for weeds to invade. These activities may include heavy foot traffic as well as vehicles traveling over the area.
 100% weed control in the lawn is impractical. Weeds will occur, but the problems can be minimized with a well-managed, vigorously growing lawn. By combining cultural methods with herbicide applications when needed, weeds will  be minimized.

For chemical control, a grassy weed in a lawn is difficult since most chemicals cannot distinguish between good and bad grass species. Fortunately, certain herbicides can distinguish between grassy plants and broadleaves. It is the chemical composition of the herbicide and the morphology of the plant that will cause certain herbicides to affect broadleaf plants but not affect grasses. Therefore, controlling broadleaf weeds in a grassy environment is relatively easy. Purchase an herbicide with the active ingredient 2,4-D, MCPP (mecoprop), or dicamba (Banvel). These products are often sold in combination, giving better management and a wider spectrum of the broadleaf weeds controlled.

For light weed infestations, spot treating is more appropriate than treating the entire lawn. Apply just enough of the solution to wet the leaf, do not apply to the point that the herbicide is dripping off the leaf. To insure maximum absorption, stop mowing 2 or 3 days before treatment and allow 3 or 4 days before mowing again. This allows sufficient time for the weeds to absorb the herbicide and transport it to their roots.
Caution: these materials are volitle, espectially 2,4-D. The drift can damage other valued broadleaf plants; tomatoes and hibiscus are particularly sensitive.