Pesticides and Vegetable Disease Control

Fungicides can be a great help in preventing diseases when properly applied to the plant foliage. Since fungicides are preventive, they should be applied before the disease occurs, or as soon as the first symptoms of disease appear. Some vegetable diseases require specific fungi- cides for their control. An outline of diseases of specific vegetables, disease description, suggested cultural and chemical control and comments follows this section.

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Fungicides are available primarily as wet- table powders, dry flowables and dusts, but a few are sold as emulsifiable concentrates, flowables and liquids. Wettable powders (WP) and dry flowable (DF) are formulated in such a manner as to be readily suspendable in water. Dusts (D) should not be mixed in water, but applied directly to the plant. Emulsifiable con- centrate (EC) fungicides contain an emulsifying agent that makes them readily suspendable in
water. Flowable (F) fungicides are finely ground wettable powders that are suspended in a liquid.
Some soil fungicides are available as gran- ules and are applied in the furrow at planting. Dust and spray fungicides may also be used as in-furrow treatments for seedling disease control.
Table II gives trade names and rates of broad spectrum fungicides for controlling foliar dis- eases of vegetables. Applying foliar fungicides to vegetables is best done by spraying, because it provides coverage of all plant surfaces. Foliar fungicides are available in dust formulations, but dusts are usually not as effective as sprays.

Outline for Control of  Vegetable Diseases

1   Common names are  used  for  chemical recommendations. Trade names are  listed in  Table II.

2   Consult label for  precise rate of application. The  rates given in  teaspoon or tablespoon per  gallon in  the  publication are  only  approximate

and  the  label of the  specific  product to  be  used  should be  consulted before  mixing and  applying any  fungicide.

3   PHI  (pre-harvest interval) is  the  minimum number of days  between last application and  harvest Never attempt to use  dust formulations of fungicides  in  spray solutions. Dusts will  not  suspend in the  spray solution. Wettable powder  formula- tions may  appear similar to dusts, but  they are formulated to be suspended in  spray solutions.

Table II. Common Names and Trade Names of  Chemicals for Controlling Diseases of  Vegetables

1   Follow  label instructions when mixing and  applying fungicides. One  gallon of fungicide spray will usually cover  400-450  square feet  of garden area (130-150  linear feet  in  three foot wide  rows).  The application rate varies with plant size.  Some  product labels stipulate higher quantities of weaker sprays than other similar products. Always follow  the  label. Labels may  limit the  number of applica- tions or the  total allowable amount of fungicide/unit area.

2  The  Environmental  Protection Agency is requiring that all  mancozeb, maneb and  metiram product registrations and  labels bearing homeowner uses  be amended to bear the  following protective clothing and  hygiene language:  “Home  gardeners applying this product must wear long-sleeved shirt, long pants and  chemical-resistant gloves.  The  gloves  must be washed thoroughly with soap  and  water before removing. Clothes must be changed immediately after using these EBDC  products and  must be laundered separately from  other laundry items before  reuse.”

This  listing does  not  imply any  preference or discrimination to other products of similar suitable composition, but  is provided solely  as  a reference. All  formulations of a particular  fungicide may  not be labeled for all  crops;  check  label before  purchasing or using any  fungicide.

Foliar sprays will  aid  in  controlling leaf spots,  rusts, mildews, anthracnose and  fruit rots. Foliar sprays are  not effective against  vascular wilts or root  rots.  Foliar sprays are  protectants, because they form  a protective layer of fungicide over  the  surface of the  fruit and  foliage. Disease agents (bacteria and  fungi) that land on these fungicide coated surfaces are  killed or prevented from  infecting the  plant.

Most  fungicides are  not  effective in  inhibit- ing  disease organisms once  they have infected a plant. It is imperative that foliar fungicides be applied prior to infection of the  plant. A spray schedule should be followed  that maintains a protective fungicide layer on the  foliage and fruit during favorable infection periods. By carefully monitoring their vegetables, some gardeners can  usually delay the  first fungicide application until the  first sign  of disease. Then a 7-14  day  spray schedule should be followed. During rainy or humid weather, spray applica- tion  intervals should be shortened.

Proper pesticide mixing and spraying plays a very  important part in  achieving disease control. Most  hom  gardeners will  find  a 1-2 gallon compressed-air sprayer adequate for applying foliar sprays. A nozzle  with a cone pattern will  provide the  most  effective coverage of plant foliage. Keep  the  pressure up  to insure small spray particle size  and  good coverage.

Sprayers should be cleaned and  rinsed after each  use.  Hose-end sprayers are  not  very  effec- tive  in  applying fungicides to vegetables. Never use  the  same sprayer for fungicides and  insecti- cides  that has  been  used  for herbicides. Residues of certain types of herbicides are  very  difficult to remove from  sprayers. These residues may  cause crop  injury if a herbicide-contaminated sprayer is used  in  applying fungicides or insecticides.

Homeowners should protect themselves when mixing or applying pesticides. Always read the label for use directions and precaution statements. As of spring 1992,  the  Environmental Protec- tion  Agency is requiring that all  mancozeb, maneb and  metiram product registrations and  labels bearing homeowner uses  be amended to bear the  following protective clothing and hygiene language:

“Home gardeners applying this product must wear long-sleeved shirt, long pants and chemical-resistant gloves. The gloves must be washed thoroughly with soap and water before removing. Clothes must be changed immediately after using these EBDC products and must be laundered separately from other laundry items before reuse.”