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 http://www.ctahr.hawaii.edu/site/info.aspx

• 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.

Rats in Fruit Trees

Hollowed out oranges, papaya, bananas and other fruits, whether hanging on the tree or on the ground, are definitely signs of rat feeding.  In Hawaii, there are four rodents that cause economic hardship: the roof or black rat, the Norway or brown rat, the Polynesian or Hawaiian rat, and the house or field mouse. In addition, they are carriers of contagious diseases including plague, murine typhus, leptospirosis, and salmonellosis. Today, most notably, they are part of the disease cycle known as Rat-Lungworm. See health.hawaii.gov/docd/disease_listing/rat-lungworm-angiostrongyliasis/  for more information and prevention of this serious condition.

Rodent control is not easy due to their ability to adapt to changes and their capacity to reproduce.

Rats are nocturnal. They have excellent memories and very repetitious habits. They are easily frightened of new things placed in their environment. The roof rat is most pronounced in this tendency. Rats have a keen sense of smell and hearing, and only a fair sense of sight with the ability to see in the dark.

Besides the hollowed out fruits, other common signs of rats are droppings, rubmarks, gnawings, nests, and unpleasant odors.  

                                                         Rat Damage on Oranges - UC IPM

In controlling these pests around the home, the first step is to clean up the environment by removing accesses to food and shelter. Physical barriers such as screens may need to be installed. When only a few rats are involved, trapping can be successful, both live and snap traps. Devices that kill rats by electrocution (e.g., Rat Zapper or Victor Electronic traps) are expensive but effective.

Paraffin-type bait blocks containing anticoagulants are also effective in controlling rats. They appeal to the rats gnawing instinct, especially those blocks with numerous ridges. Baits should be replaced immediately as they are eaten, since a single feeding on the first generation anticoagulants such as diphacinone, will not control rats; multiple doses over several successive days is required. The newer “second-generation” compounds such as brodifacoum, bromadiolone, difenacoum, and difethialone, which can be fatal after a single feeding. Prepackaged, ready-to-use bait stations containing some of these toxicants can be purchased by homeowners. 
   

Some poisons have a secondary effect which will affect animals that consume dead or nearly dead rodents. Thus, it is imperative that strict safety precautions be used in the placement and disposal of poison baits for rodents.

For more information on rats see the UC IPM website, http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74106.html