Agriculture Reference
In-Depth Information
same physiological age. This pruning should also remove all of the last season's
panicles, which inhibit future fl owering. This pruning should not be extensive;
(ii) a balanced fertilization programme that ensures good vegetative growth
but does not provide excessive amounts of nitrogen, or lead to a defi ciency;
and (iii) soil moisture management that involves limiting irrigation as the
leaves approach maturity to prevent the potential for premature shooting.
CHECKING VEGETATIVE GROWTH
Limiting vegetative growth can be achieved with paclobutrazol and
uniconazole, the latter being ten times more potent. These products are
expensive, sometimes dii cult to fi nd in most countries and if used improperly
can cause permanent tree damage. These anti-gibberellin compounds inhibit
sprouting and reduce the time needed between synchronization pruning
and fl oral stimulation by about 1 month. These inhibitors are applied 1-2
months after harvest, when the shoots from the synchronization pruning
have completed their growth phase. Paclobutrazol can be applied at a rate of
5-8 g/plant or 1 g/m of canopy diameter, while uniconazole is applied at a
rate of 0.1 g/m 2 of the canopy shade. The application is made in 10-20 l of
water put in a shallow trench at the canopy drip line; the soil should be moist
before application and irrigated after, to carry the chemicals to the root zone.
Another anti-gibberellin product, 'Pix' (mepiquat chloride), is sprayed at 1%
active ingredient on to the canopy until run of . A 2-3 cm girdle can induce
fl owering but often leads to the death of ~5% of branches per year and is not
recommended. Controlled scoring is now used on subterminal branches with
little danger of tree damage. Controlling water stress is dii cult in the tropics
with frequent rain, except in tropical deserts.
Spraying fl owering stimulants
Flowering can also be infl uenced by nitrates, such as potassium nitrate at
2-4%, calcium nitrate at 1-3% and ammonium nitrate at 1-2% sprayed
on trees in the tropics, but apparently not in the subtropics. One to three
additional sprays of the same chemicals can be done at weekly intervals if
the ef ect is not satisfactory. Thiourea can be used instead of nitrates. Young
shoots (1.25 months from bud emergence) of the Philippine cvs 'Carabao'
and 'Pahutan' can be induced to fl ower uniformly by spraying 10 and 40 g/l
of KNO 3 , respectively. 'Carabao' fl owered in 11 days, while 'Pahutan' required
20 days. Spraying older 'Carabao' shoots (8.5 months from bud emergence)
with 10-160 g/l KNO 3 induced 100% fl owering, with unsprayed controls
remaining vegetative (Bondad and Apostol, 1979). Genetic dif erences among
seedling trees and between cultivars means that variations in response to the
chemical used occur, with the nitrate ion being the ef ective ion (Nagao and
Nishina, 1993).
Eight factors will determine the success of these nitrate sprays: (i) the
leaves have to be mature, dark green and brittle when squeezed; (ii) the
 
Search WWH ::




Custom Search