Very Hungry Caterpillars by Patty G. Leander

cabbage-worm-damage

Caterpillars bring insatiable appetites to the vegetable garden.

Along with colorful butterflies, smaller and more ordinary looking moths flit around the vegetable garden this time of year, laying eggs that hatch into caterpillars whose sole purpose is to eat and excrete. If you are growing brassicas your plants have probably already been under attack by these very hungry caterpillars.

Cross-striped-caterpillar-cabbage-looper

Cross-striped caterpillar (left) and cabbage looper (right).

The main culprits here in Texas are the cabbage looper (mottled brown moth with a small white marking on each wing), cross-striped caterpillar (brownish-gray moth with darker brown spots) and cabbageworm (whitish-yellow moth with a single black dot on each wing).

cross-striped-cabbageworm-eggs

What looks like a small yellow blob (less than 1/8 inch across) on the back of a broccoli leaf is actually a mass of cross-striped caterpillar eggs waiting to hatch.

These creatures are stealth; I seldom notice the moths that lay the eggs (they are more active at night) and the freshly hatched caterpillars are so miniscule and blend so well into the foliage that they can do severe damage before they are detected. Inspect your plants often, especially on the underside of leaves; if you miss them you may be surprised to find your plants decimated the next morning.

cabbage-worm

As the caterpillar grows so does its appetite.

Though these tiny munchers are good at camouflage there is one sure way to affirm their presence before too much damage is done: miniature dark green balls of excrement. Yep, what goes in must come out and caterpillars are prolific poopers.

caterpillar-poop

Dark green droppings mean caterpillars are feasting nearby.

And the bigger they get the more they eat and the more they eat the more they poop. I have had more than one novice gardener tell me that they thought those little green balls were eggs, but if you look above or near the excrement you will almost assuredly find a caterpillar or two or three chewing away.

If you only have a few plants a good defense is to hand pick and destroy caterpillars or infested leaves every time you inspect your plants, but if you have many plants an insecticide will be more effective and a more efficient use of your time. Bacillus thuringiensis (Bt for short) is the recommended control for caterpillars, especially in the earliest stages of growth. It is an organic insecticide made from a naturally occurring bacteria found in soil; when caterpillars ingest the Bt-coated leaves it destroys their gut, causing them to stop feeding and die within a couple of days.

cabbage-worms-bt

Note the tiny egg mass inside the black circle (left); so tiny yet so destructive (right).

 

Bt is only effective against caterpillars; it will not harm humans, cats, dogs or beneficial insects but it will kill any caterpillars that ingest it, including butterfly larvae, so apply it only to edibles that are being damaged. Be sure to follow label instructions for application rate and frequency as follow-up applications may be necessary for control. Bt is sold under different trade names, including Dipel and Thuricide, and can be applied as a spray or a dust. Liquid Bt seems to roll off some of the thick, waxy leaves of cabbage, kale and collards, so I have found it beneficial to apply Bt as a dust.

Dustin-Mizer

The Dustin Mizer is a good tool for applying Bt as a dust.

Several years ago my brother gave me a tool called the Dustin Mizer that I use quite often for this purpose. When cranked it emits a fine dusting of powder over and under the plant.  It is especially important to direct Bt to the underside of the leaves as that is where the caterpillars are usually feeding.

It’s always a good idea to vary insect control methods in the vegetable garden so consider alternating Bt with a product containing the active ingredient spinosad (also derived from a soil bacterium and also organic). One other option is to use lightweight floating row cover to protect cabbage crops; cover plants as soon as they go in the ground so the moth never has access to the plants to lay her eggs.

 

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Week 38 Tips for the Zone 9 Garden

Well, I have a problem.  All of the broccoli and cabbage transplants that I put out a couple of weeks ago are now gone.  Something has eaten every last one of them.  So, this weekend I will be replanting and trying to figure out how to control whatever it is that is eating my brassicas.  Since I will be applying organic pesticides this weekend I thought this would be a good opportunity to review some of the major organic herbicides and pesticides available to the home gardener.

While our chickens eat a lot of bugs I still have to spray things like Bt and spinosad from time to time

While our chickens eat a lot of bugs I still have to spray things like Bt and spinosad from time to time

BUG CONTROL

  • Bt– Bacillus thuringiensis has been used to kill soft bodied pests in the organic garden for a very long time. I suspect that what is eating my broccoli is either a little green caterpillar called the cabbage worm or another green caterpillar called the cabbage looper.  Both of these pests can be controlled fairly well with Bt.  Like all pesticides, organic or not, Bt should be mixed for a single use.  Bt rapidly degrades in the sunlight.  Because of this, spray the plant late in the evening, covering all areas of the plant where the bug will eat.  If you mix too much Bt, add more water too the mixture and leave it out in the sun.  In 48 hours the mixture will be completely inert. NOTE:  Bt does not kill pests mmediately.  You may need to apply three times to get maximum effectiveness
  • Spinosad –. If you pests are tougher than caterpillars you will need to use spinosad. Spinosad is a live bacterium that speeds up a pest’s metabolism to the point where they stop eating and die within a couple of days.  Spinosad has been shown to be effective against caterpillars, leaf miners, fire ants, hornworms and even fleas.  Like Bt, spinosad breaks down in heat and sunlight.  However, it can remain active for five to seven days.  Only use spinosad if Bt has failed as it will kill bees and other pollinators
  • Neem oil – Neem oil is a plant extract that is mostly effective against aphids and scale insects. It can kill some insects if they are covered when they are very young (rigt after hatching).  It has also been shown to prevent some insect eggs from hatching.  It is not very effective against mature beetles like stink bugs or other leaf footed bugs
Large, broad leafed weeds like thistle and dandelion can be easily controlled with acetic acid

Large, broad leafed weeds like thistle and dandelion can be easily controlled with acetic acid

WEED CONTROL

  • Acetic Acid – Acetic acid is available in concentrations up to 20%. Concentrated acetic acid is very effective on a wide range of both grassy and broadleaf weeds.  I have seen dandelions and crabgrass begin to wither 30 minutes after the initial application.  Vinegar is best when applied to young plants.  Established weeds may need a second or third application to finally kill them.  Be careful when applying vinegar.  Overspray can kill things you don’t want to die.  I use a spray bottle and a shield when spraying close to my desirable plants.  If you want to spray a wide area, then a pump sprayer works well too.
  • Horticultural Molasses – Neil Sperry recently said that Nut Sedge (grass) is the cockroach of the gardening world. I agree.  I have tried everything to control nut sedge.  This year I read an article by Howard Garrett (The Dirt Doctor) about using horticultural molasses.  Well, I tried it and it works—kind of.  While it killed all nut grass in the cracks of my brick patio, it did not do much damage to the nut grass that was growing in my beds.  I applied the molasses at full strength.

I share these posts on Our SimpleHomestead Blog Hop.  Be sure to stop by.  The “hop” has tons of great information from gardeners and homesteaders all over the world!