1. Introduction
Macadamia is a genus of four species of trees indigenous to Australia and it is part of plant
family Proteacea (Austin et al 2008). German-Australian botanist Ferdinand Von Mueller
gave the genus the name Macadamia in 1857 in honor of the Scottish Australian chemist,
medical teacher and politician John Macadam (Mueller 1857). The four species include
macadamia intergrifoliar, macadamia jansenii, ternifoliarand and macadamia tetraphylla.
The tree is commercially important for its fruit, the macadamia nut. Beaumont is a hybrid
selection from crossing two Australian natives, the smooth-shelled (M.integrifoliar) and the
rough-shelled (M.tetraphylla) (Jones and Beaumont 1937). Is it a slow growing tree which is
evergreen and has rounded canopy. It develops bright pink, pendent flowers during
flowering and reddish new leaves. It should be grown in full sun in a fertile, deep soil which
has good drainage.
Regarding the increasing number of herbicide resistant weeds and the discontentment of
farmers from influence of herbicides consumption in macadamia, developing other methods
of weed management is essential. Development of non-chemical methods in agricultural
systems is very important. Thus, non-chemical control methods should replace the chemical
ones. Apart from the consequences caused by the indiscriminate use of herbicides, the
increase in farm productivity and use of the other non-chemical methods of weed
management is necessity (Najafi, 2007). Mechanical and cultural methods are as the most
important of non- chemical ways for weed management that are inexpensive methods for
reducing weeds competition (Wehtje et al., 1984; Cardina et al., 1987, Johnson and Mullinix,
2000; Brecke and Stephanson, 2006).
Weeds compete with plants for water, light, and nutrients. In addition, weeds can reduce air
circulation in the macadamia crop and contribute to unfavourable conditions for macadamia
to be infected by pathogens. Weed management is an important component in macadamia
nut production because weeds compete for water and nutrients. They also provide shelter
for insect pests and their predators and can enhance or reduce insect damage. Weeds can
make rodent management more difficult. Weeds can also interfere with harvesting. The
orchard floor must be free of weeds to efficiently harvest nuts on the ground manually or
with machines. Effective weed control can eliminate the competitive effects of weeds and
should be based on detailed knowledge, including factors impacting performance. For
example, the same herbicide may have varying efficacy depending on the environmental
conditions at and after the application time. Other factors include absorption, translocation,
and degradation in the plant. Selection of herbicides, herbicide combinations, rates, and
application timings should be suited to the degree of weed infestation, the optimal date for
using agrochemicals, and the combination of herbicides required to eliminate a wide
spectrum of weeds. The main aim of the research is to develop innovative, effective
methods of weed control under the conditions of weed threat, which will provide a larger
spectrum of chemical agent action and result in weed control efficiency, costs, rate
reductions, and impact on the environment.
However, when tractor mowing is used, weeds over rows remain undamaged and additional
hand slashing is then needed. Tractor mowing are usually used to control the weeds
between the rows (interrow weeding), whereas manual slashing is used to remove weeds
between macadamia plants in the row (intra-row weeding) and weeds around the bushes.
1.1 Problem statement
At Clear Water Estate use of chemical methods in the control of weeds on macadamia raise
concerns on the effects on soil health, crop health, persistence in the environment and
interaction with crop nutrition. There is need to come up with a better way of weeds control
without much effects on the agro-ecosystem.
1.2 Justification
This study aims to find a way which reduce the effects of weeds without affect soil system.
Application of herbicides destroys ground cover. This left the soil without ground cover and
became prone to erosion. According to Sorensen et al continuous application of herbicide
like glyphosate reduce microbial activity. Another potential side effect of herbicide like
glyphosate is its effect on root formation. Bott and co-workers demonstrated glyphosate’s
ability to inhibit root elongation, lateral root formation, and root biomass production in
plants. It was even demonstrated that glyphosate released from dead weeds could be
absorbed through the roots of growing plants. After entering the plant system, glyphosate is
rapidly trans-located to young growing tissues of roots, where it can accumulate and inhibit
growth.
1.3 General Objective
Agronomic Evaluation of Chemical versus Mechanical Weeds control for reduce use of
herbicides in macadamia.
1.3.1 Specific Objectives
To evaluating effects of herbicides on weeds control.
To evaluate different weeds control methods.
To evaluating effects of mechanical weeds control methods.