Combine the two? No. You'll normally find instructions on the label warning against mixing with other components. Doing so can neutralize the active ingredients or compound the damage by turning them into something else. Alternate them.

And be sure to follow the label directions as to dilution and application rate. Equally important in disease control is removing all the infected foliage and disposing of it. You can't cure or eliminate it once it exists on the plants, you can only slow it down.

"hornworms and aphids, caterpillars and beetles, aphids and who knows what else"

Well the first rule of pest control is to identify the specific pest and then use the least toxic agent that lists that specific pest. Sevin doesn't usually fall into line with that guideline since it is a broad spectrum pesticide that kills as many beneficials as it does bad guys..

Unless you have 50+ plants and vary limited time hornworms and other caterpillars can just be picked off, beetles (what kind specifically) can easily be flicked into a container of soapy water, aphids can be hosed off with water, "who knows" needs to be identified, etc. So make sure it is truly necessary to bring out the big guns or you do more harm than anything.

Dave

Dithane-m45 has only very limited approval for use on food crops. Its active ingredient is mancozeb which has home-garden use restrictions of its own. If the home gardener choose to use one of the synthetic fungicides rather than an organic one then Daconil is the recommended fungicide to use.

Dithane_M45_MSDS

Daconil's label contains no such prohibition. Dithane's states: "Dithane M-45 is compatible with most commonly used agricultural fungicides, insecticides and growth regulators. When preparing tank mixes, consult spray compatibility charts or State Cooperative Extension Service specialists prior to actual use."

Most fungicides can be tank mixed with most insecticides. You can find numerous charts on the Internet prepared by agricultural universities showing any incompatibilities.

Thanks for your help!

Dave,

I found this article and was wondering if you've tried these two methods? I'm wondering if I should just abandon the chemicals and go organic, as I'd hate to kill bees with the Sevin:

Insect and Mite Control

To manage problems with aphids and mites, try a pesticide made with rhubarb leaves. Simply boil rhubarb leaves in water for 20 minutes, and when cool strain into a spray bottle. A mild dishwashing soap can be added as well. For managing leaf-chewing pests, mix up mashed chili peppers, chopped onion and a head of minced garlic. Allow to steep in water for 24 hours before straining and spraying tomato plants. To curb attacks from tomato hornworms and other leaf cutters, make a mash of marigold leaves and flowers, and soak in water for 24 hours. Strain the solids, and add another 1.5 quarts of water plus a pinch of liquid castille soap before spraying. For problems with beetles, caterpillars, whitefly and any soft-bodied insect pest, use a mix of water, cayenne peppers and chopped horseradish root.

Fungal Prevention

Fungal diseases, like powdery mildew, can be prevented using a spray made of baking soda or potassium bicarbonate, horticultural oil and water. If you don't have horticultural oil, citrus oil or molasses makes a good substitute. In addition, milk deters powdery mildew. Mix 1 part of milk to 9 parts of water in a spray bottle for easy application. Cornmeal also can be used to manage fungal infections. Mix 1 cup of cornmeal with 5 gallons of water, strain, and then spray on tomato plants. For warding off early blight, mix 2 tablespoons each of cooking oil, organic baby shampoo and baking soda with 1 gallon of water, and then spray both sides of the leaves for best prevention.

http://homeguides.sfgate.com/homemade-organic-pesticides-tomatoes-47644.html

No I have never used the rhubarb mix although I do routinely carry a spray bottle of 1 tsp of Murphy's Oil Soap in a quart of water. Some prefer using Dawn but I like the Murphy's better because it also contains some oil. It works well as a contact pesticide for any soft body insects. But in most cases you can spritz aphids off with just plain water too.

The other mixes in the article I have heard of but with the exception of a hot pepper/garlic/peppermint blend in water to repel squirrels from the tomatoes, don't use. Over the years I have found out the hard way that many of the home-made recipe sprays, if used incorrectly, can do more damage to the plant than the bugs do. So I tend to more rely on beneficial insects, hand picking, or knocking things into a bucket of hot soapy water. But there are numerous good organic pesticides available too on the market for when the infestation gets really bad..

For fungal diseases I use organic Soap Shield brand from day one and then one of the many organic copper-based sprays like Bonide Copper-Fungicide

if necessary and alternated with Neem Oil.

All fungicides, be they organic or not, are only preventatives, not cures. They slow the disease down is all. So unless you apply one from day one of planting to prevent and do it regularly the odds are you will develop one of the common fungus diseases eventually. At that point the choice is yours to make.

Dave

I tank mix fungicides and insecticides all the time and i did so when I was a pest control applicator for a commercial nursery with 300 acres. The general rule of thumb is that when mixed, there is no precipitate formed, then you are good to go. In all my years of doing this, I can not remember mixing two incompatable mixes. Saves a lot of time and work. I used to even mix IGR (Insect Growth Regulators) with other insecticides so that I would get rid of the adults and the eggs. Sometimes, I would mix these two with another fungicide.