 |
| Figure 28. A normal clean bramble leaf versus a mite-infested leaf. |
Small Raspberry Aphid, Aphis rubicola Oestlund
Large Raspberry Aphid, Amphorophora agathonica Hottes
Aphids are among the most important plant pests. This is primarily because they transmit virus diseases. The two most important aphid-transmitted viruses to the bramble industry are raspberry mosaic, transmitted by the large raspberry aphid, and raspberry leaf curl, transmitted by the small raspberry aphid.
Life History
These aphids overwinter as eggs, which hatch in May. The young aphids
mature to be winged or wingless females, which give birth to living young during
the summer. The winged form is capable of flight and can spread over great distances,
while the wingless form remains and develops on brambles where it was born.
Males are produced only in the fall. The males mate with females, which lay
overwintering eggs. The development time and number of generations produced
depend on host and weather conditions.
Cultural Control
Eliminate virus-infected wild and cultivated brambles. Plant cultivars
that are certified to be virus free. Use the cultivars that are resistant to
aphids and viruses. Maintain 150 to 300 meters (500 to 1,000 feet) between new
plantings and infected older plantings.
Spider Mites, Tetranychus spp.
Spider mites are not a problem to growers every year. However, when they are abundant and hot, dry conditions prevail over a period of time, they cause considerable concern. Because more than one species can be involved, we will rely more on the common name of spider mites than on a single species. Thus, we will discuss spider mites attacking brambles in general terms. The same spider mites are common on many different plants.
Symptoms
Mites damage the foliage as a result of their attack. The combined rasping
and sucking of all active stages mechanically disturbs the leaf tissue and also
results in sap losses from the undersurface of the leaves, which in turn yield
tiny yellow spots, giving the foliage a speckled appearance (Figure 28). Another
telltale symptom of spider mites is their ever-present webs, especially on the
lower surface of the leaf. When an infested leaf is inverted and exposed to
direct sunlight, adult mites can be seen trying to get away from the light.
However, with a 10X hand lens, eggs, webs, cast skins, and all stages of the
spider mite can be observed on the underside of an infested leaf.
|
| Figure 28. A normal clean bramble leaf versus a mite-infested leaf. |
Severe infestations may cause leaves to become brown and fall off prematurely.
Plants may be stunted, and yields may be drastically reduced where mites are
left uncontrolled.
Seasonal History and Habits
The adult female mite has eight legs and is about 0.5 mm (1/50-inch)
long, ranging from straw colored to green, brown, or orange. The male is smaller,
about 0.3 mm (1/80-inch) long, with a narrow body and pointed abdomen. Two dark
spots, composed of the food contents, show through the transparent body wall.
The body is oval in outline, covered with sparse spines. After mating, the female
begins to lay eggs at the rate of two to six per day, producing about 100 in
a little over two months. The life cycle from hatching to adult ranges from
19 days at 55°F to five days at 75°F.
Winter is passed in the adult or second nymphal stage at the base of brambles or weeds. Because many species of plants, both cultivated and uncultivated, serve as hosts, it is entirely possible that weeds may be important sources of initial infestations. As many as 10 overlapping generations may develop in a single season.