Nufarmer Africa
Nurseries of improved sweet
potato varieties
S
weet potato is considered widely as food
security crop due to its hardiness, ease of
growing and relatively low requirement for
agricultural inputs. Availability of planting material from disease-indexed origin is critical to
maintain a high production level in sweet potato. A shortage of planting material has been
indicated as one of the major constraints to production of this crop during a survey in the major production areas. The storage roots are rich
sources of energy and nutrients. Availability of
cuttings from nurseries in the main production
areas would promote production considerably.
The ARC, with funding provided by DST,
established several medium scale sweet potato nurseries with improved ARC varieties to
ensure availability of cuttings for production.
Included in the nurseries are two ARC orangefleshed sweet potato (OFSP) varieties, which
are excellent source of provitamin A especially
variety Bophelo; as well as new sweet, low water content varieties with high yield e.g. Ndou,
Mvuvhelo and Monate. The nurseries entail 2 ha
at Roodeplaat, 0.7 ha at University of Fort Hare,
1 ha at Univ of Venda, 0.2 ha at University of
Zululand. In the past season ±190000 cuttings
were issued from the nurseries for production of
improved ARC sweet potato varieties. The ARC
OFSP varieties on average have 5-10 t/ha higher
production potential than the USA varieties that
were initially promoted. The ARC new cream
varieties deliver much improved yield as well as
improved quality roots compared to land races
which are widely grown. The yield potential of
the new cream varieties is comparable to that of
the commercial variety Blesbok.
The cuttings were distributed to various
farmers/communities in the subsistence farming settlements; and government programs
such as food gardens, school gardens and government departments such as correctional ser-
vices, rural development, social development
and department of agriculture. Cuttings were
also obtained by some commercial producers
which market the sweet potatoes to the informal market (hawker market which mostly benefit rural communities).
The nursery at Roodeplaat, for instance, has
the potential to produce over 2 million cuttings
(that will provide for production of 60 hectares
of sweet potato). At an average estimated yield
of 30 t/ha at resource-farming level, this can provide 1800 tons of sweet potato. The intervention
of ARC on the supply of planting material from
disease-indexed origin is critical to maintain a
high production level and significantly contribute to improved food security, especially in rural
based production areas.
Using insects to protect cabbage
crops and ensure food security
C
abbage is an important brassica crop,
and a source of essential minerals and
vitamins used to complement the carbohydrate rich (rice, maize, etc.) diet of billions of
people around the world. It is also a cash crop
for many small scale growers, because it is easy
to grow and has a short growing season. Since
cabbage is grown and sold throughout the year,
it is a permanent target for insect pests and diseases.
The diamondback moth (DBM), Plutella
xylostella (L.), is considered the most destructive insect pest of cabbage and related crops
throughout the world. Around the world, this
pest is estimated to cost growers about US $4-6
billion in direct crop losses and management
costs annually. Chemical control is the principal method used to control its populations, but
this has led to the pest developing resistance to
virtually all chemical classes applied against it
in the field. In an effort to manage insecticide
resistance, farmers tend to spray higher doses
and/or use cocktails of several insecticides, often
spraying more than once a week. The implications of these high insecticide inputs throughout the world are: 1) it has become increasingly
difficult to successfully grow cabbage due to
high DBM resistance levels; 2) high insecticide
residues on the crop; 3) increased non-target effects on beneficial organisms.
In an effort to address food security and food
safety issues pertaining to cabbage production
in South Africa, ARC researchers have investigated several alternative control methods for DBM
of which biological control, using parasitoids,
has shown the greatest potential. Parasitoids
are insects, usually wasps, that are free-living
as adults, and the females seek host insects in,
or on, which their offspring can develop to maturity. Since the reproduction of parasitoids is
linked to their rate of discovering hosts which, in
turn, is directly proportional to parasitoid density until some threshold is reached, conservation of parasitoid populations is key to sustain-
Nufarmer Africa | September/October 2014
able management of DBM populations. At high
parasitism levels, the efficiency of parasitoids
to suppress the pest populations and protect
crop yield was as good as was obtained with the
most effective insecticide. Thus, there is no need
to apply insecticides when parasitism levels are
sufficiently high.
Parasitoids can provide the same level of
crop protection as insecticides at high parasitism levels. Thus, conservation of DBM