Postemergence herbicides target visible weeds. They are used primarily against broadleaf weeds, perennial grasses, and sedges. The chemicals 2-4d, dicamba and mecoprop are broadleaf herbicides. The have been combined in many products that control many broadleaf weeds. Look for these active ingredients in products such as Bayer All in One Weed Killer for Lawns or Green Light Wipe-Out Broadleaf Weed Killer.

Guidelines for Using Postemergence Herbicides

When choosing an herbicide, make sure that it will control the weed and that it is recommended for your turf. Before using, read the entire label and follow it precisely. The following tips will help you achieve optimum control in the spring or fall when air temperatures are between 65 and 85 degrees F. In hotter temperatures, turf damage is more likely.

At the time of treatment, soil moisture should be adequate. When drought stressed, weed control is poor and turf damage is more likely.

Mow a couple of days before or a couple of days after application. Mowing lessens the amount of surface area that the herbicide contacts.

Treat weeds when no rain is expected for at least 24 hours.

If it is windy, wait to apply herbicides of any kind. They can and will injure ornamental plants. Best results occur when weeds are young.

For acceptable control, repeat applications, 10-14 days apart, may be required.

Orange County Farm Supply will be holding an organic gardening workshop from 10 a.m. to 1 p.m. on Saturday, May 7th.

Downy mildew (fungus - Peronospora sparsa) is a highly destructive disease. Although best known as a rose disease, downy mildew will attack vegetables, other ornamentals, and fruit plants. It can completely defoliate a plant in 4-7 days and can kill the plant.

In general, high humidity and moderate temperatures favor downy mildew. Moist air from puddles, rain, or overhead watering is enough to allow the pathogen to germinate. The optimum temperature for downy mildew to spread is 65 degrees, but the spores are killed at 81 degrees or higher.

Downy mildew will first appear on upper surfaces of leaves as patches or spots. On the underside of the leaves directly below each spot, a downy or furry growth is produced. The fungus is made up of numerous branched stalks with spores on the end. Downy mildew needs a film of water on the leaves for spores to germinate.

Regular watering from overhead and thick growth from close spacing create ideal conditions for this disease, which can spread very quickly under such conditions.

Control:
Remove all infected leaves and dispose of carefully, in closed containers so the spores cannot spread.
Spray infected plants with Monterey Aliette Fungicide .
Avoid overhead irrigation at the end of the day. Try to leave enough time for the plants to dry off before nightfall.
Thin out undergrowth of plants if necessary.