Grape Moths
Namibian crop pests  #  115
Order: Lepidoptera Family: Noctuidae
March 2003. A small grape farm is expanding  north of Tsumeb town in Namibia. Previous years there had been symptoms of damage suspected to be caused by moths. The grapes mature from mid-November to February depending on the variety. This is a draft page about the investigations. Little is known about grape pests in this area.

Healthy grapes maturing,  November 2002
Early damage, mid-November 2002
All grapes damaged, December 2002

1. Damage

Symptoms
Single grapes (Vitis vinifera) in the bundle shrink as if they were punctured. The grapes turn brown like raisins. After severe attacks there are no healthy grapes left.

Early attack, November
There was only moderate damage on the early grapes that matured during mid- to late November. The moth pressure was not very high due to limited rains. 

The species we saw coming to sugar bait and lights at night were ordinary moth species and not the dreaded fruit-piercing moths.

A few large moths on grapes at night
Second attack, end of November
During the last week of November, a  more aggressive attack was noticed. At night the grape clusters were attacked by a number of moth species. There could be 5-10 moths per cluster, all sucking the grapes. 

The large well-known moths (see below) seemed to be just sucking grapes that were already punctured but may not be able to make holes by themselves. However, a  smaller moth species was actually seen punching holes in healthy grapes.

A wheelbarrow full of discarded grapes also attracted the moths
December led to a total loss of the crop
During December, the moth attack increased as seen on the photos to the right. There were lights at the farm house nearby the grape field and moths came to the lights by the thousands, also many of the grape sucking species.  The farmer tried out one of those insect traps with a high voltage grill but it soon clogged up due to the overload of insects.

During December 2002, all remaining grapes in the field  (2 ha) were destroyed by moths within a few days!

Lights at the farm house attracted thousands of moths every night.

2. Moth species

The farmer, a researcher from Tsumeb and the amateur entomologist investigated the moth problem.  We held several night trips to the grape field to investigate what went on a night. Sugar bait and lights were used to collect moths and during inspection of sugar bait one could also see moths sucking directly on the grape bundles. The entomologist lives 300 km away and could therfore only spend some weekend nights in the field so we only have limited information about species yet. An effort was made, however, to collect specimens of the various moths involved.
 

1. Sundowner Moth (Sphingomorpha chlorea)
Wingspan 65 mm. Foodplants: Acacia, Azanza, Burkea and other trees

2. Cream Striped Owl (Cyligramma latona}
Wingspan 60-70 mm. Foodplants: Acacia

3. Green Drab (Ophiusa tirhaca)
Wingspan 55 mm. Foodplants: Combretum, Rhus, Viburnum
and many others

4. Achaea sp. possibly A. catella??.
Wingspan 50 mm. 

 

5. Catapult moth (Serrodes partita)
Wingspan 60 mm. Foodplants: Grewia, jasmine and Pappea (wild plum). A few of this fruit piercing moth were seen in Tsumeb town, only 10 km from the farm.

6. Unknown moth
Wingspan 35 mm. Dark grey with black lines. Hindwings are whitish with a dark band along the edge. This species pierce the grapes.

3 Control discussion

The moths

At first, we thought the damage was caused by fruit-piercing moths. These are moths that have a specially adapted strong proboscis that enables them to pierce the skin of fruits. "Crop Pests in Southern Africa" (Bulletin 411) lists a number of these species as: Othreis materna, Oraesia (Calpe) provocans, Serrodes partita and Dugaria scandulata. Some of these names have since changed, but we have illustrations of most of them and would be able to recognize them.

After having monitored the grapes at night we believe that a complex of 6-8 moth species are involved in the destruction of grapes. No.1 Sphingomorpha chloera was the more dominant species together with No.4 Acahea species. No.2 Cyligramma latona is common all over northern Namibia and was found early in the season but seemed to diminish in numbers later on. The No.6 Unknown moth was quite interesting as it was seen actually piercing the fresh grapes and thereby paving the way for other species. There could be up to ten of this moth on each bundle of grapes. 

The caterpillars of these moth species live and feed on wild plants in the neighbourhood and do not feed on the grapes as such. The moths are excellent flyers so they enter the grape fields at night when grapes are ripening. Next morning they may be hiding in the vegetation waiting for another night of sucking.

More collection and night watching is needed to better understand the species involved and their fluctuation over the season. We need to have them properly identified and preferably know which of them are primary fruit-piercing moth and which species can only suck grapes that are already punctured. It is also important to find out if all the species are attracted to lights which could become an important control method.

Changing cropping season

After this season's disaster, the farmer considered changing cropping season as much as possible. He believes he can get the early varieties through at end of November with only moderate losses and still harvest some grapes. By using different pruning and management techniques he will then try to manipulate the remaining varieties to produce grapes much later in the rainy season to skip the high moth pressure around December. 

Using light traps

The entomologist believes more in using light traps. It seems all of the species we saw were eagerly attracted to lights. The farm house had only solar panels at that time but electricity will be installed soon. The simplest method would be to place a number of mercury lamps in the grape field to attract the moths at night. The lamps should be placed low over white plastic trays filled with soap water. Moths would circle around the bulbs and drown in the water. The lamps must be on every night in the beginning of the season to reduce the number of moths in the grape plantation.

We tried to place a wash basin under the farm's wall-mounted lamps and it caught many moths despite the less than ideal setting. See also the photos above where there are many dead moths in the red basin.

Using Neem extract as repellant ?

No one has tried it out but it may be considered to spray the bundles of grapes with the natural extract from neem seeds. It may disguise the smell of ripening grapes and is known to be a repellant for other species. Neem trees are now found on many sites in northern Namibia and produce seeds twice a year - the main peak is January while there is a second, smaller production of seeds just before the winter.
 

Conclusion

At present there is only a few farmers (one?) around Tsumeb who grow grapes on a larger scale, but others have shown interest in making plantations in the area due to the success of grape fields in Southern Namibia. From this example, where a crop of 2 hectares was wiped out by moths in a few days, it is clear that we must find a way of controlling the moths in grapes before large investments are made.
 


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