Bumble bee Troubleshooting
Something not looking right? Work through this guide before you call us.
Zonda bumblebee hives are proven performers, and the vast majority of growers get excellent results. But hives are living systems, and occasionally things don’t go as expected. This guide walks you through the most common causes of poor performance, and what to do about them — step by step.
Work through these checks in order. Most issues are resolved at Step 1 or 2.
First: Understand Where Your Hive Is in Its Lifecycle
Before troubleshooting, check how old your hive is. Bumblebee colonies follow a natural lifecycle — they build up, peak, then wind down. What looks like a problem may simply be a hive that is young, or one that has reached the end of its productive life.
Hives should be replaced approximately every six weeks. If your growing area is larger than 1,500 m², consider running a second hive alongside to maintain consistent pollination coverage.
| Hive Age | Expected Status | What to Expect |
|---|---|---|
| Under 7 days | Building up | Low activity is normal — colony is settling in |
| 7–14 days | Active | Good foraging activity and visible flower marking |
| 14–28 days | Peak performance | Maximum colony size and foraging activity |
| 28–42 days | Declining | Colony naturally winding down — plan replacement |
| 42+ days | End of life | Replace hive. Colony has completed its natural cycle |
The number of bees foraging in the crop at any given time is also influenced by conditions inside the hive and the time of year. As a general guide, expect roughly one foraging bee per 100 plants, or around 150 workers, at peak activity.
Note: Bumblebee hives can vary considerably in activity level. A hive that appears quieter than another is not necessarily underperforming — always use flower marking (see Step 1) as your primary guide to pollination effectiveness.
STEP 1
Check for Flower Marking
This is the single most reliable indicator of whether your hive is doing its job. When a bumblebee visits a tomato flower and vibrates it (buzz pollination), it leaves a visible brown mark on the flower. These marks confirm that the flower has been pollinated.
Check several plants across the crop. Look for brown marks on the flowers — they can be fresh (light brown) or older (darker). Both indicate successful pollination visits.
If you can see consistent flower marking across the crop — you do not have a bee problem. Even if activity looks low, the hive is working effectively. Move on only if marking is absent or patchy.
A useful benchmark: at good pollination levels, you should see marking on 300 or more flower visits per assessment. If marking is well below this, or absent entirely, continue to Step 2.
STEP 2
Diagnose Why Bees Are Not Visiting Flowers
If flower marking is absent or insufficient, there are several possible causes. Work through each one below.
Bees are foraging outside the greenhouse
This is one of the most common causes of poor in-crop marking. If bees can access the outside environment, they will often prefer natural flower sources over crop flowers — particularly in spring when wildflowers are abundant.
You can identify this by checking whether bees are flying toward the roof or walls of the greenhouse rather than down into the crop. If so:
- Ensure all vents, gaps and entry points are screened
- Try temporarily closing the hive entrance during peak morning foraging hours to redirect bees to the crop
- If the problem persists, contact Zonda for guidance
Crop flowers are not attractive to bees
Bees are selective. If the crop flowers are providing little nectar or pollen — due to plant stress, high temperatures, or the crop stage — bees may be reluctant to forage on them. This can also occur at very high or very low greenhouse temperatures, or during periods of very rapid plant growth.
Check plant health and growing conditions. Address any stress factors (water, nutrition, temperature) and reassess over the following 24–48 hours.
The hive is active but bees will not fly
If you can see bees at the hive entrance or inside the hive but they are not flying into the crop, the most likely cause is a disruption to foraging behaviour. This is often linked to pesticide exposure — even contact with residues from previous applications can temporarily disrupt foraging. Check:
- Whether any pesticides, fumigants or biological control agents have been applied recently
- Whether neighbouring properties have sprayed herbicides or other chemicals
- Whether burners or heaters are running correctly (see Pollution section below)
If the hive has been contaminated, bees may recover over several days. In severe cases, the hive may need to be replaced. Contact Zonda if you are unsure.
The hive is too weak
Colonies naturally decline in the second half of their lifecycle. A weak hive is not necessarily a failed hive — it may simply be nearing the end of its productive period. Check the hive age table above.
If the hive is less than four weeks old and appears very weak (very few bees, little activity at any time of day), contact Zonda — your hive may be covered under the four-week performance guarantee.
STEP 3
Check Environmental Factors (Misset)
‘Misset’ is the term used when flowers are being visited by bees but fruit is still not forming correctly. It means the flowers are being pollinated, but something in the growing environment is preventing successful fertilisation and fruit development.
If you have good flower marking but poor fruit set, work through the following environmental factors:
- Temperature — too high or too low for pollen germination
- Light levels — insufficient light reducing plant energy for fruit set
- Plant balance — overly vigorous growth diverting energy from fruit
- Humidity — too high or too low, affecting pollen viability
- Fertilisation — excess or deficiency affecting flower quality
- Pollution — chemical or gas contamination in the growing environment
Temperature
Temperature has a direct effect on pollen germination. If the greenhouse is too cold or too hot, pollen may fail to germinate even when deposited correctly on the stigma.
Below 11°C, many crops will slow or stop setting fruit altogether. At very high temperatures (above 35°C), pollen viability drops sharply.
The most important factors are greenhouse temperature and humidity. Use these target ranges as a guide:
Daytime temperature: 18–26°C is optimal. Pollen germination slows below about 14°C and drops sharply above 30°C; above 35°C, viability collapses.
Night temperature: 15–18°C.
Relative humidity: aim for 60–80% during flowering. Above 90% pollen grains clump and fail to transfer; below 50% pollen dries out and loses viability.
For commercial growers running VPD setpoints
Many commercial greenhouses are managed against a target vapour pressure deficit (VPD), sometimes referred to as a “VD” setpoint. The two settings below are common reference points — VD2 for cooler greenhouse environments and VD7 for warmer ones. Each table shows the temperature and relative humidity combinations that hit that target.
VD2 — Cooler Greenhouse Regime
| Temperature (°C) | Relative Humidity |
|---|---|
| 15–17°C | 80% |
| 18–23°C | 85% |
VD7 — Warmer Greenhouse Regime
| Temperature (°C) | Relative Humidity |
|---|---|
| 15–18°C | 50% |
| 19–20°C | 55% |
| 21–22°C | 60% |
| 23–24°C | 65% |
| 25–26°C | 70% |
| 27–28°C | 75% |
| 29–30°C | 80% |
If you’re unsure which regime suits your crop and climate, contact Zonda or your agronomist for guidance.
The optimal temperature range for most greenhouse tomato pollination is 18–26°C. Outside this range, fruit set can decline even with good bee activity and flower marking.
Plant Balance
Overly vigorous plants — those producing very large, lush leaves and rapid stem growth — may not be producing enough sugars to support fruit development. In this state, the plant effectively diverts energy into vegetative growth at the expense of fruit set.
Signs of imbalance include: very dark green, large leaves; rapid internode extension; soft, watery stems; and poor fruit set despite adequate pollination. Address plant balance through irrigation management, nutrition adjustment, and crop loading. Your agronomist can advise on the right strategy for your crop.
Light Level
Low light — particularly during winter months or in heavily shaded greenhouses — reduces the plant’s capacity for photosynthesis and therefore the energy available for fruit development. Even well-pollinated flowers may fail to set in persistently low-light conditions.
If light is limiting, consider supplementary lighting or adjusting your crop management to reduce leaf shading.
Humidity
Very high humidity (above 90%) can cause pollen grains to clump and fail to transfer effectively. Very low humidity (below 50%) can cause pollen to dry out and lose viability. Aim to maintain greenhouse humidity between 60–80% during the flowering period for best results.
Fertilisation
Heavy fertilisation — particularly nitrogen — can contribute to the plant imbalance described above, as well as directly affecting flower quality. Excess fertilisation may cause flowers to drop before fruit can form. If misset coincides with recent changes to your nutrition programme, review your fertiliser rates and conduct a soil or substrate analysis.
Pollution and Chemical Contamination
Several airborne contaminants can disrupt bee activity and pollen viability. Check for the following:
- Herbicide drift from neighbouring properties — even low-level exposure can disrupt foraging behaviour
- CO₂ acidity from poorly functioning burners — CO₂ combines with water to form carbonic acid, which can affect both plant and bee health
- Ammonia from fertilisers — releasing ammonium gas in enclosed environments can be harmful to bees
- Nitrous oxides from poorly burning heaters or gas equipment
If you suspect pollution is a factor, check all heating and burning equipment, ventilate the greenhouse, and contact Zonda for further guidance.