Asparagus has a number of major insect and disease pests. It is my intention to add pest pictures to this module as the opportunity arrises. The first pests often encountered by asparagus growers are cutworms. They come in two varieties: white and dark-sided. The white cutworm over-winters as a larva and begins feeding immediately upon emergence of the spears. White cutworms climb and generally damage only the tips. Severe winters like the one we experienced in 2004-2005 can cause high mortality in this variety of cutworm. Dark-sided cutworm on the otherhand over winter as eggs and don't generally become a problem until a couple of weeks into the harvest season. This cutworm feeds at or below the soil surface and causes the spears to crook or twist. In cold, slow growth harvest years like 2005 insecticides that were applied before harvest to control white cutworms may have disappated by the time white cutworms arrive. The picture below is of a dark-sided cutworm. Black cutworms are less common, but not unknown in asparagus. They generally show up even later than dark-sided cutworms.
COMMON ASPARAGUS BEETLE:
The major asparagus insect pest during the fern growing season is common asparagus beetle. The larvae of this pest, known locally as "slugs" are voracious feeders. If left unchecked common asparagus beetle larvae will strip asparagus fern leaving it brown and dessicated. The following picture is of a common asparagus beetle larvae blown up 40 times.
Common Asparagus Beetle Larvae 8/2/05
Pete Babbin of Hart Coop brought me my first aecial rust spores of the season. The aecial rust spore is the first stage we see on asparagus in the spring. While it does not spread rapidly, it does give birth to the uredial spore which does spread rapidly. Some growers like to treat this stage on young fields in order to limit the amount of uredial lesions later in the season. Folicur is the recommended control. We have a Section 18 Label already in place for that product. You can obtain a copy from the Vegetable Area of Expertise Website. The following pictures are of aecial rust lesions magnified 40x and 140x.
Uredial rust lesions are the rapidly spreading type of lesion. They appear in mid to late June and are a threat to asparagus fern. The image below is below is blown up by a factor of about 50X. Uredial lesions are often confused with stemphyllium purple spot lesions, especially before the lesion breaks open to release the rusty colored spores. The easiest way to tell the difference is between purple spot lesions and uredial rust lesions is that rust lesions are alway raised, while purple spot lesions are always sunken. The EPA has granted a Section 18 Label for Folicur in Michigan for the 2005 growing season. This fungicide is highly affective in treating this disease since it has some back action against new lesions. Please use the link in the Vegetable Production section to visit the Vegetable Area of Expertise Team website and obtain a copy of the Section 18 Folicur Label. Federal law requires that you have a copy of this label in hand when you treat. Chlorothalonil and several EBDC fungicides are also labeled, but only as protectants.
Uredial Rust Lesion: 7/22/05
Once cool nights are common, usually in the late summer or early fall. Uredial lesions change over to the over-wintering or Tellial stage. This stage is not infective, but if warm weather comes back for a prolonged period of time these lesions can turn back into the Uredial lesion. A common mistake that growers often make is that when Uredial lesions turn from red to black they assume they have been burned out with fungicide, while in reality the have just moved over in to the Tellial stage. The following picture is of new Tellial Lesions.
Tellial Rust Lesion 8/2/05
STEMPHYLLIUM PURPLE SPOT:
This foliar asparagus disease is the more common of the two major diseases attacking asparagus fern in Michigan. It is less damaging than rust, but also harder to treat effectively. The fungicide chlorothalonil, has a federal label for treatment of this disease in asparagus. However, it is a protectant and does very little good if the disease has severely infected a plant. The EBDC class of fungicides also give some protection from the disease, but MSU trials show that they are half as affective as chlorothalonil. The disease is favored by high temperatures and periods of prolonged leaf wettness. Below are two pictures of stemphyllium lesions on fern talks. Defoliation does not usually occur until lesions appear on the small branches or cladophylls.
Stemphyllium Purple Spot Lesions 7/22/05