Note: Timings listed are effective but all may not be required for control. Timings used will depend upon orchard history of disease, length of bloom, and weather conditions each year.

Brown rot: Flowers are susceptible beginning with the emergence of the sepals (green bud) until the petals fall.

Russet scab: A physiological disorder, no pathogens involved.

Dormant applications of an organophosphate insecticide plus narrow range oil control a wide range of pests - peach twig borer, San Jose scale and the eggs of aphids (mealy plum and leaf curl) and European red and brown almond mites. The oil is important, it helps the insecticide penetrate the target insects or eggs suffocating them.

Narrow range oil (4-7 gallons per acre) plus one of several organophosphate or carbamate insecticides should be used. Effective insecticides include diazinon, Supracider, Lorsban and BoSevin. Here are important guidelines for effective spray application:

• Use a ground rig, not aircraft.
• Drive slowly, 1.5 to 2.0 mph.
• Spray damp trees (from fog) but not dripping wet trees.
• In large trees, two-thirds of the spray material should go into the upper one-half of the tree.
• Spray material should dry on the tree before a rain.
• For dilute sprays in mature trees, apply 200-400 gal/A. When applied correctly, concentrate sprays are effective too.
• Do not apply sprays containing oil to prunes when fully dormant. Wait until after February 15 and preferably delay treatments until bud swell.

Dormant Spray Alternatives

Using Bt: Bacillus thuringiensis (Bt) applied prebloom and at bloom is effective as a substitute for "hard" pesticides normally applied during the dormant season for control of peach twig borer (PTB). Bt must be applied twice during bloom: The first application is put on at the "popcorn" stage, and the second 7 to 10 days later. Bt must be applied by ground rig. It is compatible with fungicides timed for brown rot and shothole control at those stages of bloom. Remember, Bt does not kill San Jose scale, aphids, or mite eggs.

Alternate Year Dormant Sprays: Applying a dormant spray every other year has been as effective in controlling scale and peach twig borer as annual treatments in our experiments. If this strategy is used, good spray coverage is essential in the year of treatment; the objective is to reduce the pest level to the point it cannot recover to do economic damage in the year of no dormant spray.

Aphids (mealy plum and leaf curl) are not controlled with Bt or in the year no dormant spray is applied in an alternate year strategy. Populations may or may not develop in such orchards. As trees leaf out and grow into April, careful monitoring is needed to detect and treat aphid populations before damage occurs. Aphid outbreaks occur in spots within orchards and favor young and vigorously growing trees. If treatment is required, spray oil or an insecticide with good coverage is effective control.

What About Bees This Year???

Bees are required to transfer pollen from a prune flower's anther to its stigma for ultimate fruit set. In absence of bee activity, little fruit set occurs.

Prunes bloom in mid-March when weather conditions for bee flight and activity are usually good. Under good weather conditions, many growers' experiences have shown that resident bee populations (not rented bees) are sufficient for crop set. Placing bees in an orchard, however, maximizes its fruit set potential. In many cases, especially when weather is good, an overcropping situation can result and must be dealt with later. Overcropping and potential for small fruit size is unprofitable and expensive to manage. The question is whether to rely on native bee population to set the crop or place bees in the orchard; usually bee keepers provide bees free to prune growers.

Place bees if:

1. You are in an isolated location, away from other fruit orchards.
2. You have not observed significant resident bee populations in the past.
3. Forecast weather conditions may be unfavorable for bee flight.
4. Young orchards coming into bearing.
5. Bloom appears sparse.

Do not place if:

1. Your experience has been that the crop sets adequately with native bees (in other words, there's a lot of bees around).
2. Trees have not been pruned and imminent bloom appears heavy.
3. Neighbors have hives placed in their orchards.

Controlling Ground Squirrels with Burrow Fumigants

With the onset of spring, ground squirrels emerge from their winter hibernation. Soon after, they begin to breed, and before you know it you have a squirrel problem on your hands.

The most cost-effective management strategy for ground squirrels is to control them before they have a chance to reproduce. Every female killed early in the season means about 8 fewer young to remove later if the control is delayed until young are active aboveground.

In early spring, fumigating burrows is one of the most effective means of control. Fumigants work best at this time of year because soil moisture is relatively high, helping to retain a high concentration of the lethal gases in the burrow system. Do not fumigate while squirrels are still hibernating because the squirrel plugs its burrow with soil, preventing fumes from reaching the nest chamber. The plug cannot be seen by examining the burrow entrance.

You have 3 choices when it comes to fumigants:

(1) Gas cartridges:

Gas cartridges are cylinders of combustible ingredients with a fuse. When ignited, they emit smoke and toxic gases. The cartridge is placed in the burrow entrance, the fuse lit, and the cartridge pushed well back into the burrow with a shovel handle. The opening is then sealed off with sod or soil and tamped lightly.

(2) Aluminum phosphide:

Aluminum phosphide tablets or pellets react with atmospheric and soil moisture to produce phosphine gas which is lethal to all mammals. The label recommended number of tablets are placed in the burrow entrance. Crumpled newspaper is placed in the opening to prevent soil from covering the tablet and the entrance filled with sod or soil which is tamped firmly. Aluminum phosphide is a restricted use material and should be handled accordingly.

(3) Acrolein (Magnacide "H"):

Acrolein is an aquatic herbicide which has vapors that, in high concentration, are quite toxic to mammals. This volatile liquid is applied to the burrow system through a hose with a specially constructed wand calibrated to deliver a precise dose. The burrow entrances are then sealed with sod or soil. Acrolein is a restricted use material that can only be used by licensed Pest Control Operators.

With all fumigants it is necessary to examine the treated area about 3 days following the applicant to determine if any survivors have dug out. All opened holes should be retreated and sealed.

One way to conserve fumigants is to first fill in all of the burrow entrances with sod or soil. After about 3 days, squirrels will reopen their burrow systems. Fumigants need only be applied to active burrows.

As with any pesticide, it is important to read and follow label instructions with particular regard for safety factors and nontarget species. Gas cartridges have the potential to produce flames so should not be used where a significant fire hazard exists such as near buildings, dry grass, or other flammable materials. To avoid the accumulation of fumes in enclosed areas, never fumigate beneath buildings or in burrows that may open under occupied buildings.

Be aware of the signs of nontarget species such as kit foxes or burrowing owl inhabiting abandoned ground squirrel burrows. Do not treat a burrow if you suspect a nontarget animal is present. County agricultural commissioners can provide additional information on how to recognize active ground squirrel burrows.

Further information on ground squirrel control may be obtained from the county agricultural commissioner.